题目内容
One might expect that the vacuum would always be the state of the lowest possible energy for a given region of space. If an area is initially empty and a real panicle is put into it, the total energy, it seems, should be raised by at least the energy equivalent of the mass of the added panicle. A surprising result of some recent theoretical investigations is that this assumption is not invariably true. There are conditions under which the introduction of a real particle of finite mass into an empty region of space can reduce the total energy, If the reduction in energy is great enough, an electron and a positron will be instantly created. Under these conditions the electron and positron are not a result of vacuum fluctuations but are real particles, which exist indefinitely and can be detected. In other words, under these conditions the vacuum is an unstable state and can decay(衰减) into a state of lower energy; that is one in which real particles are created.
The necessary condition for the decay of the vacuum is the presence of an intense electric field. As a result of the decay of the vacuum, the space permeated by such a field can be said to obtain an electric charge, and it can be called a charged vacuum. The particles that materialize in space make the charged vacuum likely to be found in only one place: in the immediate vicinity of a super heavy atomic nucleus(原子核), one with about twice as many pro tons as the heaviest natural nuclei known. A nucleus that large cannot be stable, but it might be possible to assemble one next to a vacuum for long enough to observe the decay of the vacuum. Experiments attempting to achieve this are now under way.
Which of the following titles best describes the passage as a whole？
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听力原文： Social Security is one of the great moral achievements of American government. For almost 70 years, it has kept millions of elderly citizens out of poverty and assured young Americans of a secure future. The Social Security system is essential, yet it faces a long-term problem.
While benefits for today's seniors are secure, the system is headed towards bankruptcy down the road. Each year there are more retirees taking money out of the system, and not enough additional workers to support them.
In the 1950s, there were about 16 workers paying for every Social Security beneficiary. Today, there are about three. And eventually, there will only be two workers per beneficiary. These changes signal a looming danger. In the year 2018, for the first time ever, Social Security will pay out more in benefits than the government collects in payroll taxes. And the gaps will grow larger each year leading to the bankruptcy of the system.
Therefore, Social Security is not a personal savings plan. Benefits paid to today's retirees come directly from the taxes paid by today's workers. The crisis in Social Security can be avoided by emphasizing several principles. First, nothing will change for those who are receiving Social Security and for those who are near retirement. Secondly, payroll taxes will not increase, because higher taxes would slow economic growth. More efforts must be made to use the power of compound interest, by giving younger workers the option to save some of their payroll taxes in a personal account, which government cannot take away.
(30)
What does the example of India illustrate？
Man's puzzlement and preoccupation with time both derive ultimately from his unique relationship to it. All animals exist in time and are changed by it; only man can control it.
Like Proust, the French author whose experiences became his literary capital, man can recapture the past. He can also summon up things to come, displaying imagination and foresight along with memory. It really can be argued, that memory and foresightedness are the essence of intelligence; that man's ability to manipulate time, to employ both past and future as guides to present action, is what makes him human.
To be sure, many animals can react to time after a fashion. A rat can learn to press a lever that will, after a delay of some 25 seconds, reward it with a bit of food. But if the delay stretches beyond 30 seconds, the animal is stumped. It can no longer associate the reward so "far" in the future with the present lever-pressing.
Monkeys, more smart than rats, are better able to deal with time. If one of them is allowed to see food being hid den under one of two cups, it can pick out the right cup even after 90 seconds have passed. But after that time interval, the monkey's hunt for the food is no better than chance predicts.
With the apes, man's nearest cousins, "time sense" takes a big step forward. Even under laboratory conditions, quite different from those they encounter in the wild, apes sometimes show remarkable ability to manipulate the present to obtain a future goal. A chimpanzee, for example, can learn to stack two boxes, one on the other, as a platform. from which it can reach a hanging banana. Chimpanzees, indeed, carry their ability to deal with the future to the threshold of human capacity: they can make tools. And it is by the making of tools—physical tools as crude as a stone chopper, mental tools as subtle as a mathematical equation—that man characteristically prepares for future contingencies.
Chimpanzees in the wild have been seen to strip a twig of its leaves to make a probe for extracting termites from their hole. Significantly, however, the ape does not make his tool before setting out on a termite hunt, but only when it actually sees the insects or their nest. Here, as with the banana and the crates, the ape can cope only with a future that is immediate and visible—and thus halfway into the present.
According to the article, which of the following statements is TRUE？
Section A
Directions: In this section, you will hear 8 short conversations and 2 long conversations. At the end of each conversation, one or more questions will be asked about what was said. Both the conversation and the questions will be spoken only once. After each question there will be a pause. During the pause, you must read the four choices marked A, B, C and D, and decide which is the best answer.
听力原文：M: I think the whole class is going on the field trip next Friday.
W: I'm not so sure, not everyone has paid the transportation fee.
Q: What does the woman imply？
(12)
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