单选集


? ? Antibiotic resistance doesn’t just make pathogens(病原体) difficult to treat, It also makes them harder to track Traditionally, epidemiologists(流行病专家)following the paths of disease-causing microbes have identified their suspects by features of bacterial polysaccharide(多糖) coats, susceptibility to different antibiotics, or other schemes But these tracking techniques "are losing their relevance (相关性,实用性), "says Alexander Tomasz, a microbiologist at Rockefeller University in New York City. With the increase in drug resistance, a variety of resistant microbes can now wear the same coat or be resistant to the same drugs, making it harder and harder to keep tabs on individual strains (菌株).
? ? Epidemiologists, therefore, are increasingly turning to more precise molecular typing techniques, such as DNA fingerprinting, to distinguish resistant strains.
? ? DNA typing tools are, of course, not new. Indeed, some DNA-based methods, such as comparing plasmids (质体)(small rings of DNA outside the chromosomes 〈染色体〉), have been used by epidemiologists to track infections since the 1970s. but since plasmid DNA is transferred easily and often between different strains, that technique too has its limitations.
? ? ?More recent techniques use restriction enzymes to cut apart entire bacterial chromosomes into strain-specific fragment patterns, Another method uses specific radiolabeled (放射标汇的) DNA probes, in a technique known as Southern hybridization(杂交), to test for the presence of a particular drug-resistance gene in a bacterial strain. "Such tools give epidemiologists, unprecedented resolving power for identifying reservoirs and transition routes of genes and pathogens, "says Tomasz. That has helped researchers track a number of drug-resistant clones as they travel vast distances.
? ? ?Such tracking methods also "help us learn about the mechanism of resistance, "says CDC(疾病控制和预防中心) epidemiologist Robert Breiman. Resistance grows, he explains, either as one resistant organism spreads from one location to the next—as in the Brazilian MRSA(耐甲氧苯青素金黄色葡萄球菌)—or as different strains and even species of microbes share the genes responsible for drug resistance, as a series of studies of vancomycin(万古霉素) resistance recently demonstrated.
? ? That knowledge also helps public health officials combat the spread. If resistance spreads "horizontally’as a microbe increases its range, Breiman says it’s important to focus prevention efforts on minimizing person-to-person spread in hospitals and day-care centers. If, however, resistance genes are jumping between organisms, that suggests that overly aggressive antibiotic treatment is encouraging nonresistant bugs to acquire new genes. "In such cases, the focus needs to be on controlling anti-microbial use, "says Breiman. The hoped-for result: fewer infections to track.
It is of vital importance to concentrate prevention efforts on minimizing person-to-person spread.

A:A．

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B:B．
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 C:C．
Not mentioned


? ? Antibiotic resistance doesn’t just make pathogens(病原体) difficult to treat, It also makes them harder to track Traditionally, epidemiologists(流行病专家)following the paths of disease-causing microbes have identified their suspects by features of bacterial polysaccharide(多糖) coats, susceptibility to different antibiotics, or other schemes But these tracking techniques "are losing their relevance (相关性,实用性), "says Alexander Tomasz, a microbiologist at Rockefeller University in New York City. With the increase in drug resistance, a variety of resistant microbes can now wear the same coat or be resistant to the same drugs, making it harder and harder to keep tabs on individual strains (菌株).
? ? Epidemiologists, therefore, are increasingly turning to more precise molecular typing techniques, such as DNA fingerprinting, to distinguish resistant strains.
? ? DNA typing tools are, of course, not new. Indeed, some DNA-based methods, such as comparing plasmids (质体)(small rings of DNA outside the chromosomes 〈染色体〉), have been used by epidemiologists to track infections since the 1970s. but since plasmid DNA is transferred easily and often between different strains, that technique too has its limitations.
? ? ?More recent techniques use restriction enzymes to cut apart entire bacterial chromosomes into strain-specific fragment patterns, Another method uses specific radiolabeled (放射标汇的) DNA probes, in a technique known as Southern hybridization(杂交), to test for the presence of a particular drug-resistance gene in a bacterial strain. "Such tools give epidemiologists, unprecedented resolving power for identifying reservoirs and transition routes of genes and pathogens, "says Tomasz. That has helped researchers track a number of drug-resistant clones as they travel vast distances.
? ? ?Such tracking methods also "help us learn about the mechanism of resistance, "says CDC(疾病控制和预防中心) epidemiologist Robert Breiman. Resistance grows, he explains, either as one resistant organism spreads from one location to the next—as in the Brazilian MRSA(耐甲氧苯青素金黄色葡萄球菌)—or as different strains and even species of microbes share the genes responsible for drug resistance, as a series of studies of vancomycin(万古霉素) resistance recently demonstrated.
? ? That knowledge also helps public health officials combat the spread. If resistance spreads "horizontally’as a microbe increases its range, Breiman says it’s important to focus prevention efforts on minimizing person-to-person spread in hospitals and day-care centers. If, however, resistance genes are jumping between organisms, that suggests that overly aggressive antibiotic treatment is encouraging nonresistant bugs to acquire new genes. "In such cases, the focus needs to be on controlling anti-microbial use, "says Breiman. The hoped-for result: fewer infections to track.
This enzyme manufactures prostaglandins, substances that cause pain and inflammation.

A:A．

Right ? ? ? ? ? ? ? ? ? ?
B:B．
Wrong ? ? ? ? ? ? ? ? ?
 C:C．
Not mentioned


? ?1. ? ?AIDS is the final, life-threatening stage of infection with human immuno-deficiency virus(HIV). AIDS stands for acquired immuno-deficiency syndrome. The name refers to the fact that HIV severely damages the patient’s disease-fighting immune system. Cases of AIDS were first identified in 1981 in the United States, but researchers have traced cases to as early as 1969. Millions of AIDS cases have been diagnosed worldwide.
? ?2. ? ?AIDS is caused by two viruses that belong to a group called retroviruses. The first AIDS virus was isolated by researchers in France in 1983 and researchers in the United States in 1984. This virus became known as HIV-1. in 1985, scientists in France identified another closely related virus that also produces AIDS. This virus, named HIV-2, occurs mainly in Africa. HIV-1 occurs throughout the world.
? ?3. ? ? People infected with HIV eventually develop symptoms that also may be caused by other, less serious conditions. With HIV infection, however, these symptoms are prolonged and often more severe. They include enlarged lymph glands, tiredness, fever, loss of appetite and weight, diarrhea, yeast infections of the mouth and vagina, and night sweats.
? ?4. ? ? An HIV-infected person may develop AIDS from 2 to 15 or more years after becoming infected. In children born with HIV infection, this interval is usually shorter. A few people who have been infected with HIV for more than 15 years have not developed any symptoms or suffer only minor symptoms. An infected person can transmit the virus to another person whether or not symptoms are present. Infection with HIV appears to be lifelong in all who become infected.
? ?5. ? ? Researchers have identified three ways in which HIV is transmitted: sexual intercourse, direct contact with infected blood, and transmission from an infected woman to her fetus or baby. The most common way of becoming infected is through intimate sexual contact with an HIV-infected person. In the United States, sexual transmission of HIV has occurred mainly among homosexual men, but it is becoming more frequent among heterosexual men and women.
? ?6. ? ? People who inject drugs into their bodies can be exposed to infected blood by sharing hypodermic needles, syringes, or equipment used to prepare drugs for injection. Health-care workers can become infected with HIV by coming into direct contact with ?infected blood. This may occur through injury with a needle or other sharp instrument used in treating an HIV-infected patient. A few patients have become infected while receiving treatment from an HIV-infected dentist.
? ?7. ? ? An infected pregnant woman can transmit the AIDS virus to her fetus even if she has no symptoms. Transmission may also occur from an HIV-infected mother to her baby through breast-feeding.
? ?8. ? ? Studies indicate that HIV is not transmitted through air, food, or water, or by insects. No known cases of AIDS have resulted from sharing eating utensils, bathrooms, locker rooms, living space, or classrooms.


? ?1. ? ?AIDS is the final, life-threatening stage of infection with human immuno-deficiency virus(HIV). AIDS stands for acquired immuno-deficiency syndrome. The name refers to the fact that HIV severely damages the patient’s disease-fighting immune system. Cases of AIDS were first identified in 1981 in the United States, but researchers have traced cases to as early as 1969. Millions of AIDS cases have been diagnosed worldwide.
? ?2. ? ?AIDS is caused by two viruses that belong to a group called retroviruses. The first AIDS virus was isolated by researchers in France in 1983 and researchers in the United States in 1984. This virus became known as HIV-1. in 1985, scientists in France identified another closely related virus that also produces AIDS. This virus, named HIV-2, occurs mainly in Africa. HIV-1 occurs throughout the world.
? ?3. ? ? People infected with HIV eventually develop symptoms that also may be caused by other, less serious conditions. With HIV infection, however, these symptoms are prolonged and often more severe. They include enlarged lymph glands, tiredness, fever, loss of appetite and weight, diarrhea, yeast infections of the mouth and vagina, and night sweats.
? ?4. ? ? An HIV-infected person may develop AIDS from 2 to 15 or more years after becoming infected. In children born with HIV infection, this interval is usually shorter. A few people who have been infected with HIV for more than 15 years have not developed any symptoms or suffer only minor symptoms. An infected person can transmit the virus to another person whether or not symptoms are present. Infection with HIV appears to be lifelong in all who become infected.
? ?5. ? ? Researchers have identified three ways in which HIV is transmitted: sexual intercourse, direct contact with infected blood, and transmission from an infected woman to her fetus or baby. The most common way of becoming infected is through intimate sexual contact with an HIV-infected person. In the United States, sexual transmission of HIV has occurred mainly among homosexual men, but it is becoming more frequent among heterosexual men and women.
? ?6. ? ? People who inject drugs into their bodies can be exposed to infected blood by sharing hypodermic needles, syringes, or equipment used to prepare drugs for injection. Health-care workers can become infected with HIV by coming into direct contact with ?infected blood. This may occur through injury with a needle or other sharp instrument used in treating an HIV-infected patient. A few patients have become infected while receiving treatment from an HIV-infected dentist.
? ?7. ? ? An infected pregnant woman can transmit the AIDS virus to her fetus even if she has no symptoms. Transmission may also occur from an HIV-infected mother to her baby through breast-feeding.
? ?8. ? ? Studies indicate that HIV is not transmitted through air, food, or water, or by insects. No known cases of AIDS have resulted from sharing eating utensils, bathrooms, locker rooms, living space, or classrooms.
Paragraph 3 ______.


? ?1. ? ?AIDS is the final, life-threatening stage of infection with human immuno-deficiency virus(HIV). AIDS stands for acquired immuno-deficiency syndrome. The name refers to the fact that HIV severely damages the patient’s disease-fighting immune system. Cases of AIDS were first identified in 1981 in the United States, but researchers have traced cases to as early as 1969. Millions of AIDS cases have been diagnosed worldwide.
? ?2. ? ?AIDS is caused by two viruses that belong to a group called retroviruses. The first AIDS virus was isolated by researchers in France in 1983 and researchers in the United States in 1984. This virus became known as HIV-1. in 1985, scientists in France identified another closely related virus that also produces AIDS. This virus, named HIV-2, occurs mainly in Africa. HIV-1 occurs throughout the world.
? ?3. ? ? People infected with HIV eventually develop symptoms that also may be caused by other, less serious conditions. With HIV infection, however, these symptoms are prolonged and often more severe. They include enlarged lymph glands, tiredness, fever, loss of appetite and weight, diarrhea, yeast infections of the mouth and vagina, and night sweats.
? ?4. ? ? An HIV-infected person may develop AIDS from 2 to 15 or more years after becoming infected. In children born with HIV infection, this interval is usually shorter. A few people who have been infected with HIV for more than 15 years have not developed any symptoms or suffer only minor symptoms. An infected person can transmit the virus to another person whether or not symptoms are present. Infection with HIV appears to be lifelong in all who become infected.
? ?5. ? ? Researchers have identified three ways in which HIV is transmitted: sexual intercourse, direct contact with infected blood, and transmission from an infected woman to her fetus or baby. The most common way of becoming infected is through intimate sexual contact with an HIV-infected person. In the United States, sexual transmission of HIV has occurred mainly among homosexual men, but it is becoming more frequent among heterosexual men and women.
? ?6. ? ? People who inject drugs into their bodies can be exposed to infected blood by sharing hypodermic needles, syringes, or equipment used to prepare drugs for injection. Health-care workers can become infected with HIV by coming into direct contact with ?infected blood. This may occur through injury with a needle or other sharp instrument used in treating an HIV-infected patient. A few patients have become infected while receiving treatment from an HIV-infected dentist.
? ?7. ? ? An infected pregnant woman can transmit the AIDS virus to her fetus even if she has no symptoms. Transmission may also occur from an HIV-infected mother to her baby through breast-feeding.
? ?8. ? ? Studies indicate that HIV is not transmitted through air, food, or water, or by insects. No known cases of AIDS have resulted from sharing eating utensils, bathrooms, locker rooms, living space, or classrooms.
Paragraph 4 ______.


? ?1. ? ?AIDS is the final, life-threatening stage of infection with human immuno-deficiency virus(HIV). AIDS stands for acquired immuno-deficiency syndrome. The name refers to the fact that HIV severely damages the patient’s disease-fighting immune system. Cases of AIDS were first identified in 1981 in the United States, but researchers have traced cases to as early as 1969. Millions of AIDS cases have been diagnosed worldwide.
? ?2. ? ?AIDS is caused by two viruses that belong to a group called retroviruses. The first AIDS virus was isolated by researchers in France in 1983 and researchers in the United States in 1984. This virus became known as HIV-1. in 1985, scientists in France identified another closely related virus that also produces AIDS. This virus, named HIV-2, occurs mainly in Africa. HIV-1 occurs throughout the world.
? ?3. ? ? People infected with HIV eventually develop symptoms that also may be caused by other, less serious conditions. With HIV infection, however, these symptoms are prolonged and often more severe. They include enlarged lymph glands, tiredness, fever, loss of appetite and weight, diarrhea, yeast infections of the mouth and vagina, and night sweats.
? ?4. ? ? An HIV-infected person may develop AIDS from 2 to 15 or more years after becoming infected. In children born with HIV infection, this interval is usually shorter. A few people who have been infected with HIV for more than 15 years have not developed any symptoms or suffer only minor symptoms. An infected person can transmit the virus to another person whether or not symptoms are present. Infection with HIV appears to be lifelong in all who become infected.
? ?5. ? ? Researchers have identified three ways in which HIV is transmitted: sexual intercourse, direct contact with infected blood, and transmission from an infected woman to her fetus or baby. The most common way of becoming infected is through intimate sexual contact with an HIV-infected person. In the United States, sexual transmission of HIV has occurred mainly among homosexual men, but it is becoming more frequent among heterosexual men and women.
? ?6. ? ? People who inject drugs into their bodies can be exposed to infected blood by sharing hypodermic needles, syringes, or equipment used to prepare drugs for injection. Health-care workers can become infected with HIV by coming into direct contact with ?infected blood. This may occur through injury with a needle or other sharp instrument used in treating an HIV-infected patient. A few patients have become infected while receiving treatment from an HIV-infected dentist.
? ?7. ? ? An infected pregnant woman can transmit the AIDS virus to her fetus even if she has no symptoms. Transmission may also occur from an HIV-infected mother to her baby through breast-feeding.
? ?8. ? ? Studies indicate that HIV is not transmitted through air, food, or water, or by insects. No known cases of AIDS have resulted from sharing eating utensils, bathrooms, locker rooms, living space, or classrooms.
Paragraph 5 ______.


? ?1. ? ?AIDS is the final, life-threatening stage of infection with human immuno-deficiency virus(HIV). AIDS stands for acquired immuno-deficiency syndrome. The name refers to the fact that HIV severely damages the patient’s disease-fighting immune system. Cases of AIDS were first identified in 1981 in the United States, but researchers have traced cases to as early as 1969. Millions of AIDS cases have been diagnosed worldwide.
? ?2. ? ?AIDS is caused by two viruses that belong to a group called retroviruses. The first AIDS virus was isolated by researchers in France in 1983 and researchers in the United States in 1984. This virus became known as HIV-1. in 1985, scientists in France identified another closely related virus that also produces AIDS. This virus, named HIV-2, occurs mainly in Africa. HIV-1 occurs throughout the world.
? ?3. ? ? People infected with HIV eventually develop symptoms that also may be caused by other, less serious conditions. With HIV infection, however, these symptoms are prolonged and often more severe. They include enlarged lymph glands, tiredness, fever, loss of appetite and weight, diarrhea, yeast infections of the mouth and vagina, and night sweats.
? ?4. ? ? An HIV-infected person may develop AIDS from 2 to 15 or more years after becoming infected. In children born with HIV infection, this interval is usually shorter. A few people who have been infected with HIV for more than 15 years have not developed any symptoms or suffer only minor symptoms. An infected person can transmit the virus to another person whether or not symptoms are present. Infection with HIV appears to be lifelong in all who become infected.
? ?5. ? ? Researchers have identified three ways in which HIV is transmitted: sexual intercourse, direct contact with infected blood, and transmission from an infected woman to her fetus or baby. The most common way of becoming infected is through intimate sexual contact with an HIV-infected person. In the United States, sexual transmission of HIV has occurred mainly among homosexual men, but it is becoming more frequent among heterosexual men and women.
? ?6. ? ? People who inject drugs into their bodies can be exposed to infected blood by sharing hypodermic needles, syringes, or equipment used to prepare drugs for injection. Health-care workers can become infected with HIV by coming into direct contact with ?infected blood. This may occur through injury with a needle or other sharp instrument used in treating an HIV-infected patient. A few patients have become infected while receiving treatment from an HIV-infected dentist.
? ?7. ? ? An infected pregnant woman can transmit the AIDS virus to her fetus even if she has no symptoms. Transmission may also occur from an HIV-infected mother to her baby through breast-feeding.
? ?8. ? ? Studies indicate that HIV is not transmitted through air, food, or water, or by insects. No known cases of AIDS have resulted from sharing eating utensils, bathrooms, locker rooms, living space, or classrooms.
People with HIV infection usually develop AIDS______.


? ?1. ? ?AIDS is the final, life-threatening stage of infection with human immuno-deficiency virus(HIV). AIDS stands for acquired immuno-deficiency syndrome. The name refers to the fact that HIV severely damages the patient’s disease-fighting immune system. Cases of AIDS were first identified in 1981 in the United States, but researchers have traced cases to as early as 1969. Millions of AIDS cases have been diagnosed worldwide.
? ?2. ? ?AIDS is caused by two viruses that belong to a group called retroviruses. The first AIDS virus was isolated by researchers in France in 1983 and researchers in the United States in 1984. This virus became known as HIV-1. in 1985, scientists in France identified another closely related virus that also produces AIDS. This virus, named HIV-2, occurs mainly in Africa. HIV-1 occurs throughout the world.
? ?3. ? ? People infected with HIV eventually develop symptoms that also may be caused by other, less serious conditions. With HIV infection, however, these symptoms are prolonged and often more severe. They include enlarged lymph glands, tiredness, fever, loss of appetite and weight, diarrhea, yeast infections of the mouth and vagina, and night sweats.
? ?4. ? ? An HIV-infected person may develop AIDS from 2 to 15 or more years after becoming infected. In children born with HIV infection, this interval is usually shorter. A few people who have been infected with HIV for more than 15 years have not developed any symptoms or suffer only minor symptoms. An infected person can transmit the virus to another person whether or not symptoms are present. Infection with HIV appears to be lifelong in all who become infected.
? ?5. ? ? Researchers have identified three ways in which HIV is transmitted: sexual intercourse, direct contact with infected blood, and transmission from an infected woman to her fetus or baby. The most common way of becoming infected is through intimate sexual contact with an HIV-infected person. In the United States, sexual transmission of HIV has occurred mainly among homosexual men, but it is becoming more frequent among heterosexual men and women.
? ?6. ? ? People who inject drugs into their bodies can be exposed to infected blood by sharing hypodermic needles, syringes, or equipment used to prepare drugs for injection. Health-care workers can become infected with HIV by coming into direct contact with ?infected blood. This may occur through injury with a needle or other sharp instrument used in treating an HIV-infected patient. A few patients have become infected while receiving treatment from an HIV-infected dentist.
? ?7. ? ? An infected pregnant woman can transmit the AIDS virus to her fetus even if she has no symptoms. Transmission may also occur from an HIV-infected mother to her baby through breast-feeding.
? ?8. ? ? Studies indicate that HIV is not transmitted through air, food, or water, or by insects. No known cases of AIDS have resulted from sharing eating utensils, bathrooms, locker rooms, living space, or classrooms.
HIV is transmitted in three ways: sexual intercourse, transmission from an infected woman to her fetus or baby and______.


? ?1. ? ?AIDS is the final, life-threatening stage of infection with human immuno-deficiency virus(HIV). AIDS stands for acquired immuno-deficiency syndrome. The name refers to the fact that HIV severely damages the patient’s disease-fighting immune system. Cases of AIDS were first identified in 1981 in the United States, but researchers have traced cases to as early as 1969. Millions of AIDS cases have been diagnosed worldwide.
? ?2. ? ?AIDS is caused by two viruses that belong to a group called retroviruses. The first AIDS virus was isolated by researchers in France in 1983 and researchers in the United States in 1984. This virus became known as HIV-1. in 1985, scientists in France identified another closely related virus that also produces AIDS. This virus, named HIV-2, occurs mainly in Africa. HIV-1 occurs throughout the world.
? ?3. ? ? People infected with HIV eventually develop symptoms that also may be caused by other, less serious conditions. With HIV infection, however, these symptoms are prolonged and often more severe. They include enlarged lymph glands, tiredness, fever, loss of appetite and weight, diarrhea, yeast infections of the mouth and vagina, and night sweats.
? ?4. ? ? An HIV-infected person may develop AIDS from 2 to 15 or more years after becoming infected. In children born with HIV infection, this interval is usually shorter. A few people who have been infected with HIV for more than 15 years have not developed any symptoms or suffer only minor symptoms. An infected person can transmit the virus to another person whether or not symptoms are present. Infection with HIV appears to be lifelong in all who become infected.
? ?5. ? ? Researchers have identified three ways in which HIV is transmitted: sexual intercourse, direct contact with infected blood, and transmission from an infected woman to her fetus or baby. The most common way of becoming infected is through intimate sexual contact with an HIV-infected person. In the United States, sexual transmission of HIV has occurred mainly among homosexual men, but it is becoming more frequent among heterosexual men and women.
? ?6. ? ? People who inject drugs into their bodies can be exposed to infected blood by sharing hypodermic needles, syringes, or equipment used to prepare drugs for injection. Health-care workers can become infected with HIV by coming into direct contact with ?infected blood. This may occur through injury with a needle or other sharp instrument used in treating an HIV-infected patient. A few patients have become infected while receiving treatment from an HIV-infected dentist.
? ?7. ? ? An infected pregnant woman can transmit the AIDS virus to her fetus even if she has no symptoms. Transmission may also occur from an HIV-infected mother to her baby through breast-feeding.
? ?8. ? ? Studies indicate that HIV is not transmitted through air, food, or water, or by insects. No known cases of AIDS have resulted from sharing eating utensils, bathrooms, locker rooms, living space, or classrooms.
An HIV-infected mother may transmit the AIDS virus to her fetus through______.

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