There are several advantages in making computers as small as one can. Sometimes weight is particularly important. A modern aircraft, for example, carries quite a load of electronic apparatus. If it is possible to make any of these smaller, and therefore lighter, the aircraft can carry a bigger pay-load. This kind of consideration applies to space satellites and to all kinds of computers that have to be carried about.
But weight is not the only factor. The smaller the computer the faster it can work. The signals go to and fro at a very high but almost constant speed. So if one can scale down all dimensions to, let us say, one tenth, the average lengths of the current-paths will be reduced to one tenth. So, very roughly speaking, scaling down of all linear dimensions in the ratio of one to ten also gives a valuable bonus: the speed of operation is scaled up 10 times. Other techniques allow even further speed increases.
This increase of operation is a real advantage. There are some application in which computers could be used which require very fast response times. Many of these are military, of course; but military applications also have applications in engineering sooner or later. For example, automatic blind landing of aircraft requires continuous computer calculations which result in control of the aircraft flight. The more immediate the responses are, the more stable that control can be.
Another advantage is that less power is required to run the computer. In space vehicles and satellites this is an important matter; but even in a trial application we need not waste power. Sometimes a computer takes so much power that cooling systems which require still more power have to be installed to keep the computer from getting too hot, which would increase the risk of faults developing. So a computer which does not need to be cooled saves power on two counts.
Another advantage is reliability. Mini-computers have been made possible by the development of integrated circuits. Instead of soldering bits of wire to join separate components such as resistors and capacitors sometimes in the most intricate networks, designers can now produce many connected circuits in one unit which involves no soldering and therefore no risk of broken joints at all.
If all linear dimensions of a computer is scaled down to one tenth, ______.

A:the speed of its operation will go up ten times B:the electric signals will go to and fro ten times faster C:its operation speed will remain constant D:its weight will be reduced to one tenth

Text 2

If all linear dimensions of a computer is scaled down to one tenth, ______.

A:the speed of its operation will go up ten times B:the electric signals will go to and fro ten times faster C:its operation speed will remain constant D:its weight will be reduced to one tenth

Facial expressions carry meanings that are partly determined by culture. For example, many Japanese do not show their emotions as freely as Americans do, so teachers in the United States sometimes have trouble knowing whether their Japanese students understand and enjoy their lessons.
Another example is the smile. As a common facial expression, it may show affection, convey politeness, or disguise(掩饰)true feelings. But in different cultures. smiles have different meanings. Many people in Russia consider smiling at strangers in public to be unusual and even a suspicious behavior. Yet many Americans smile freely at strangers in public places, for American culture a smile is typically an expression of pleasure. Therefore some Russians believe that Americans smile in the wrong places; some Americans believe that Russians don’t smile enough. In Southeast Asian cultures, a smile is frequently used to cover emotional pain or embarrassment. Vietnamese people may tell the sad story of how they had to leave their country but end the story with a smile.

（　）American teachers sometimes have trouble understanding Japandse students in class because Japanese students （　）

A:do not show their emotions as freely as American stydents do B:are similar to American students in showing emotions C:only express their emotions when permitted D:do not know what to say

Most of the pioneers of low-temperature physics expected gases to liquefy, but none of them predicted superconductivity. This phenomenon was discovered in 1911 by Onnes while he was studying frozen mercury.
More than 40 years passed before physicists were able to offer an explanation for superconductivity. The accepted theory, developed in the 1950s, holds that the fundamental behavior of electrons changes at very low temperatures because of the effects of quantum mechanics. Electrons are tiny particles that make up the outer part of an atom, circling rapidly around the nucleus of the atom. In a regular conductor—a metal that conducts an electric current—the outermost electrons are not bound tightly to the atoms, and so they move around relatively freely. The flow of these electrons is an electric current.
At normal temperatures, a conductor’s electrons cannot move completely freely through the metal because they are "bumped around" by the metal’s atoms. But according to the leading theory of superconductivity, when a metal is very cold, electrons form pairs. Then, like couples maneuvering on a crowded dance floor but never colliding, the paired electrons are able to move unimpeded through the metal. In pairing up, it seems, the electrons are able to "blend together" and move in unison without resistance.This explanation seems to account for superconductivity at extremely low temperatures, but in 1986 scientists in Switzerland found that some metal-containing ceramics are superconductors at much higher temperatures. By 1992, scientists had developed ceramics that become superconducting at - 297’F, and some researchers speculated that room-temperature superconductors may be possible. Scientists are still trying to formulate a theory for high-temperature superconductivity.The new ceramic materials can be maintained at their superconducting temperatures, with relatively inexpensive liquid nitrogen rather than the much colder and much more costly liquid helium required by metal superconductors. The cost difference could make superconductivity practical for many new technologies. For example, magnetically levitated trains, which require superconducting electromagnets, would be much cheaper to build than they are now. Superconducting devices might also be used for advanced power transmission lines and in new types of compact, ultrafast computers. But for the time being, superconductivity is finding application mostly in scientific research and in some kinds of medical imaging devices.

At very low temperatures, superconductivity in a metal occurs where（　）.

A:electrons do not move freely through the metal B:electrons are crowded together C:paired electrons move uninterruptedly D:paired electron dance together to and fro

{{B}}第二篇{{/B}}

At very low temperatures, superconductivity in a metal occurs where______.

A:electrons do not move freely through the metal B:electrons are crowded together C:paired electrons move uninterruptedly D:paired electron dance together to and fro

Regeneration of Limbs Most people would agree that it would be wonderful if humans could regenerate limbs. Those who have lost their arms or legs would be complete again. The day is still far off when this might happen. But in the last 10 years, doctors have reported regeneration in smaller parts of the body, most often fingers. Regeneration is not a newly-discovered process. For centuries, scientists have seen it work in some kinds of animals. Break off a lizards (蜥蜴的) tail, for example, and it will grow a new tail. Scientists now are looking for a way to turn on this exciting ability in more highly-developed animals, including humans. Their experiments show that nerves, cell chemistry and the natural electric currents in the body all seem to have a part in this process. The body of every animal contains general purpose cells that change into whatever kind of cells the body needs. Animals such as the lizard or salamander (蝾螈) use these cells to regenerate a new tail or leg when the old one is broken off. These cells collect around the wound. They form a mass called a blastema (胚基). The cells of the blastema begin to change. Some become bone cells, some muscle cells, some skin cells. Slowly, a new part re-grows from the body outward. When completed, the new part is just like the old one. More than 200 years ago, Italian scientist Luigi Spallanzani showed that younger animals have a greater ability to regenerate lost parts than older animals. So do animals lower on the ladder of evolutionary development. The major difference seems to be that less-developed animals have more nerves in their tails and legs than humans do in their arms and legs. Another helpful piece of information was discovered in the late 1800s. Scientists found that when a creature is injured, an electrical current flows around the wound. The strength of the current depends on how severe the wound is and on how much nerve tissue is present. In 1945, American scientist Meryl Rose tested another idea about regeneration. He thought a new limb might grow only from an open wound. Doctor Rose cut off the front legs of some frogs, below the knee. He kept the wounds wet with a strong salty liquid. This prevented skin from growing over the wounds. The results were surprising. Frogs do not regenerate new legs naturally. But these frogs began to grow new limbs. About half of each cut-off leg grew back again. New bones and muscles developed. This research has led doctors to new ways of treating cut-off fingers. Doctors have observed, for example, that many children and some adults will re-grow the top of a finger if the wound is left open. In Dr. Rose’s test, frogs with cut-off legs______.

A:didn’t survive B:bled freely from their open wounds C:began to grow new limbs D:started to grow tails

The cause fro the heat in the interior of the earth is _______.

A:radioactive elements B:the great pressure of the earth C:not determined D:the heart remaining from the formation of the earth

Regeneration of Limbs
Most people would agree that it would be wonderful if humans could regenerate limbs. These who have lost their arms or legs would be complete again. The day is still far off when this might happen. But in the last 10 years, doctors have reported regeneration in smaller parts of the body, most often fingers.
Regeneration is not a newly-discovered process. For centuries, scientists have seen it work in some kinds of animals. Break off a lizard’s (蜥蜴的) tail, for example, and it will grow a new tail. Scientists now are looking for a way to turn on this exciting ability in more highly-developed animals, including humans. Their experiments show that nerves, cell chemistry and the natural electric currents in the body all seem to have a part in this process.
The body of every animal contains general purpose cells that change into whatever kind of cells the body needs. Animals such as the lizard or salamander (蝾螈) use these cells to regenerate a new tail or leg when the old one is broken off. These cells collect around the wound. They form a mass called a blastama (胚基). The cells of the blastema begin to change. Some become bone cells, some muscle cells, some skin cells. Slowly, a new part regrows from the body outward. When completed, the new part is just like the old one.
Mote than 200 years ago, Italian scientist Luigi Spallanzani showed that younger animals have a greater ability to regenerate lost parts than older animals. So do animals lower on the ladder of evolutionary development. The major difference seems to be that less-developed animals have more nerves in their tails and legs than humans do in their arms and legs.
Another helpful piece of information was discovered in the late 1600s. Scientists found that when a creature is injured, an electrical current flows around the wound. The strength of the current depends on how severe the wound is and on how much nerve tissue is present.
In 1945, American scientist Meryl Rose tested another idea about regeneration. He thought a new limb might grow only from an open wound. Doctor Rose cut off the front legs of some frogs, below the knee. He kept the wounds wet with a strong salty liquid. This prevented skin from growing over the wounds. The results were surprising. Frogs do not regenerate new legs naturally. But these frogs began to grow new limbs. About half of each cut-off leg grew back again. New bones and muscles developed.
This research has led doctors to new ways of treating cut-off fingers. Doctors have observed, for example, that many children and some adults will regrow the top of a finger if the wound is left open.

In Dr. Rose’s test, frogs with cut-off legs（　）

A:didn’t survive. B:began to grow new limbs. C:bled freely from their open wounds. D:started to grow tails.

In Dr. Rose's test, frogs with cut-off legs

A:didn't survive. B:began to grow new limbs. C:bled freely from their open wounds. D:started to grow tails.