单选题 15.The chemical adenosine is released by brain cells when those cells are active. Adenosine then binds to more and more sites on cells in certain areas of the brain, as the total amount released gradually increases during wakefulness. During sleep, the number of sites to which adenosine is bound decreases. Some researchers have hypothesized that it is the cumulative binding of adenosine to a large number of sites that causes the onset of sleep.
Which of the following, if true, provides the most support for the researchers' hypothesis?

A、 Even after long periods of sleep when adenosine is at its lowest concentration in the brain, the number of brain cells bound with adenosine remains very large.
B、 Caffeine, which has the effect of making people remain wakeful, is known to interfere with the binding of adenosine to sites on brain cells.
C、 Besides binding to sites in the brain, adenosine is known to be involved in biochemical reactions throughout the body.
D、 Some areas of the brain that are relatively inactive nonetheless release some adenosine.
E、 Stress resulting from a dangerous situation can preserve wakefulness even when brain levels of bound adenosine are high.

【正确答案】 B

【答案解析】Argument Evaluation
Situation Adenosine is released from brain cells that are active. The amount of adenosine released increases during wakefulness, and it binds to more and more sites on cells in certain brain locations. The number of sites to which it is bound decreases during sleep. Researchers have hypothesized that the cumulative binding of adenosine to many sites causes the onset of sleep.
Reasoning Which of the five pieces of information most strongly supports the hypothesis? If the hypothesis is correct, then some factor that impedes the binding of adenosine should be closely associated with wakefulness. Therefore, finding some such factor, and observing that it is accompanied by wakefulness when the factor operates, would tend to confirm the hypothesis.
A Without further, more specific information, this piece of information suffices neither to confirm nor to refute the hypothesis.
B Correct. A finding that caffeine, known to induce wakefulness, inhibits adenosine from binding to sites on brain cells helps confirm the hypothesis.
C This piece of information lacks a clear relevance to the hypothesized impact on sleep, and therefore does not help confirm the hypothesis.
D This information lacks a clear relevance to the hypothesized impact on sleep, and therefore does not help confirm the hypothesis.
E What this indicates is that stress may impede the hypothesized sleep-inducing effect of adenosine. It does not refute the hypothesis but does not confirm it either.
The correct answer is B.