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.

答案选B，看了讨论贴，还是不太懂...

推理逻辑

wakefulness-when cells active-adenosine released-bind to sites-sites accumulated to a large number-stimulate person-sleep-adenosine decrease

Most support-

关键是最支持的这个假设，那这个假设是大量由AD形成的SITE是导致睡觉的最主要原因，那要睡觉就是要形成这些SITES。如果要支持的话，就是如果这些SITES形不成，就无法导致睡眠，从而无法导致睡眠的形成，也就从反面支持了这个假设。

A 睡觉后这个AD没有下降，所以与假设相反

B 看上面解释

C 无关

D 与题目的第一句矛盾

E 提到危险的状况，与题目无关