在LD调制中，偏置电流Ib选择的原则是（）Ith

A:0.7~1 B:2 C:1.5

Many immigrants to the United States find the decision to seek better lives for their families in America can have an unexpected and tragic consequence. Deep differences with their children develop over language and culture.
"Many immigrants arrive here without much education. Their kids soon gain language skills and also street marts on how to live in America, leaving the parents at a disadvantage, " Ileana, Roses, pastor of a Methodist church group operating in Virginia, said.
"Not only that but they find they cannot relate to children who quickly absorb American culture, " she said.
According to the US Census Bureau, the number of foreign born or first generation Americans reached 55 million last year, a record one in five of the total population.
A government survey of 922 immigrants in 2000 found that nearly 40 percent of those who had been in the United States for more than 15 years would still like to take English classes if they had the time.
Two thirds of low income households depended on their children for translation.
Psychologists and sociologists say parents can lose their position of authority in a family as a result and the effects of that can be far-reaching.
Children exposed to American pop culture that glorifies youth and sexuality often rebel when their parents try to impose the conservative values they brought with them.
"Americanization erodes all important aspects of parenting, " said Richard Weissbourd, who teaches education at Harvard University.
"I feel a part of me is dying with my children. They don’t listen to my music. I have to play it on Sunday morning when they are not around, " said an immigrant.
From the passage we can infer that the population of the states at present is about ______.

A:275 million B:220 million C:255 million D:smaller than 250 million

Many immigrants to the United States find the decision to seek better lives for their families in America can have an unexpected and tragic consequence. Deep differences with their children develop over language and culture.
"Many immigrants arrive here without much education. Their kids soon gain language skills and also street marts on how to live in America, leaving the parents at a disadvantage," Ileana, Roses, pastor of a Methodist church group operating in Virginia, said.
"Not only that but they find they cannot relate to children who quickly absorb American culture," she said.
According to the US Census Bureau, the number of foreign born or first generation Americans reached 55 million last year, a record one in five of the total population.
A government survey of 922 immigrants in 2000 found that nearly 40 percent of those who had been in the United States for more than 15 years would still like to take English classes if they had the time.
Two thirds of low income households depended on their children for translation.
Psychologists and sociologists say parents can lose their position of authority in a family as a result and the effects of that can be far-reaching.
Children exposed to American pop culture that glorifies youth and sexuality often rebel when their parents try to impose the conservative values they brought with them.
"Americanization erodes all important aspects of parenting," said Richard Weissbourd, who teaches education at Harvard University.
"I feel a part of me is dying with my children. They don’t listen to my music. I have to play it on Sunday morning when they are not around," said an immigrant.
From the passage we can infer that the population of the states at present is about ______.

A:275 million B:220 million C:255 million D:smaller than 250 million

Shortages of flu vaccine are nothing new in America, but this year’s is a whopper. Until last week, it appeared that 100 million Americans would have access to flu shots this fall. Then British authorities, concerned about quality-control problems at a production plant in Liverpool, barred all further shipments by the Chiron Corp. Overnight, the U. S. vaccine supply dwindled by nearly half and federal health officials found themselves making an unusual plea. Instead of beseeching us all to get vaccinated, they’re now urging most healthy people between the ages of 2 and 64 not to. "This reemphasizes the fragility of our vaccine supply," says Dr. Martin Myers of the National Network for Immunization Information, "and the lack of redundancy in our system."
Why is such a basic health service so easily knocked out Mainly because private companies have had little incentive to pursue it. To create a single dose of flu vaccine, a manufacturer has to grow live virus in a 2-week-old fertilized chicken egg, then crack the egg, harvest the virus and extract the proteins used to provoke an immune response. Profit margins are narrow, demand is fickle and, because each year’s flu virus is different, any leftover vaccine goes to waste. As a result, the United States now has only two major suppliers (Chiron and Aventis Pasteur)—and when one of them runs into trouble, there isn’t much the other can do about it. "A vaccine maker can’t just call up and order 40 million more fertilized eggs, " says Manon Cox, of Connecticut-based Protein Sciences Corp. "There’s a whole industry that’s scheduled to produce a certain number of eggs at. a certain time."
Sleeker technologies are now in the works, and experts are hoping that this year’s fiasco will speed the pace of innovation. The main challenge is to shift production from eggs into cell cultures—a medium already used to make most other vaccines. Flu vaccines are harder than most to produce this way, but several biotech companies are now pursuing this strategy, and one culture-based product (Solvay Pharmaceuticals’ Invivac) has been cleared for marketing in Europe.
For Americans, the immediate challenge is to make the most of a limited supply. The government estimates that 95 million people still qualify for shots under the voluntary restrictions announced last week. That’s nearly twice the number of doses that clinics will have on hand, but only 60 million Americans seek out shots in a normal year. In fact, many experts are hoping the shortage will serve as an awareness campaign—encouraging the people who really need a flu shot to get one.
From the last paragraph we can infer that ______.

A:the government hopes to solve the problem by way of volunteer restrictions B:more than 47 million Americans who are qualified to get flu vaccine shots can not get them this year C:America has to deal with a limited supply of flu vaccines this year D:normally only a small percentage of American population gets flu vaccine shots each year

Many animals have an excellent sense of smell, which they use in hunting. On the other hand, their eyesight may be poor. Dogs, for example, have poor eyesight and no color vision. They see only shades of gray. But the dog’s sense of smell is extraordinary,
The kind of dog known as Alsatian has 220 million olfactory (嗅觉) cells. Man has five million. Scientists believe that the Alsatian is one million times better than man in finding out odors.
The human sense of smell, however, is really quite good. The average human being can distinguish more than 10,000 different odors.

The Alsatian’s olfactory cells are （　）times as many as man’s.

A:forty-four B:one million C:220 million D:10,000

Many animals have an excellent sense of smell, which they use in hunting. On the other hand, their eyesight may be poor. Dogs, for example, have poor eyesight and no color vision. They see only shades of gray. But the dog’s sense of smell is extraordinary,
The kind of dog known as Alsatian has 220 million olfactory (嗅觉) cells. Man has five million. Scientists believe that the Alsatian is one million times better than man in finding out odors.
The human sense of smell, however, is really quite good. The average human being can distinguish more than 10,000 different odors.

The Alsatian’s olfactory cells are （） times as many as man’s.

A:forty-four B:one million C:220 million D:10,000

Many animals have an excellent sense of smell, which they use in hunting. On the other hand, their eyesight may be poor. Dogs, for example, have poor eyesight and no color vision. They see only shades of gray. But the dog’s sense of smell is extraordinary,
The kind of dog known as Alsatian has 220 million olfactory (嗅觉) cells. Man has five million. Scientists believe that the Alsatian is one million times better than man in finding out odors.
The human sense of smell, however, is really quite good. The average human being can distinguish more than 10,000 different odors.
The Alsatian’s olfactory cells are ______times as many as man’s.

A:forty-four B:one million C:220 million D:10,000

Many immigrants to the United States find the decision to seek better lives for their families in America can have an unexpected and tragic consequence. Deep differences with their children develop over language and culture.
"Many immigrants arrive here without much education. Their kids soon gain language skills and also street marts on how to live in America, leaving the parents at a disadvantage, " Ileana, Roses, pastor of a Methodist church group operating in Virginia, said.
"Not only that but they find they cannot relate to children who quickly absorb American culture, " she said.
According to the US Census Bureau, the number of foreign born or first generation Americans reached 55 million last year, a record one in five of the total population.
A government survey of 922 immigrants in 2000 found that nearly 40 percent of those who had been in the United States for more than 15 years would still like to take English classes if they had the time.
Two thirds of low income households depended on their children for translation.
Psychologists and sociologists say parents can lose their position of authority in a family as a result and the effects of that can be far-reaching.
Children exposed to American pop culture that glorifies youth and sexuality often rebel when their parents try to impose the conservative values they brought with them.
"Americanization erodes all important aspects of parenting, " said Richard Weissbourd, who teaches education at Harvard University.
"I feel a part of me is dying with my children. They don’t listen to my music. I have to play it on Sunday morning when they are not around, " said an immigrant.
From the passage we can infer that the population of the states at present is about ______.

A:275 million B:220 million C:255 million D:smaller than 250 million