Q36

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 concen-

tration 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.

我怎么觉得都不对啊,为什么是B?

注意：

it is the cumulative binding of adenosine to a  large number of sites that

causes the onset of sleep

而Caffeine能够interfere with the binding of adenosine to sites on brain cells

所以，B是合适的

我的理解：

设A为：adenosine；B为：sleep;

原文结论说的是：有A则有B：A——> B：

adenosine累积到大量的sites时，启动了睡眠；

选项B说：没有A就没有B：无A——>无 B：

Caffeine，妨碍了adenosine累积（无A），因此人保持清醒（不想睡，既无B），从反面支持了原来的结论。

当adenosine积累到大量的site时候，这时就没有空间给adenosine再bind了即“During sleep, the number of sites to which adenosine is bound decreases”，所以睡眠开始

而B防碍了这个过程，就不能积累到“没位置积累而睡觉”