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.选B作者: 泫水清清 时间: 2011-10-27 16:43
LZ好人，大感谢作者: wangjia1203 时间: 2011-10-27 16:44
LZ好人~~有答案么作者: grenoble123 时间: 2011-10-27 16:44
B is correct作者: Sardaukar 时间: 2011-10-27 16:45
选啥，B嘛？作者: wenbo900206 时间: 2011-10-27 16:45
B~~~~~~~~~~~~~作者: fdunan 时间: 2011-10-27 16:49
GWD原题作者: angelliu2011 时间: 2011-10-27 16:50
多谢了，感动作者: luxurylove 时间: 2011-10-27 17:28
谢谢 应该是GWD的 ，PREP原题不会再出现的作者: jeffery1103 时间: 2011-10-27 18:40
GWD上的原题, 10套以后的作者: majestywhite 时间: 2011-10-27 19:29
LZ这个绝对给力啊！作者: godgodme 时间: 2011-10-27 21:11
谢谢LZ!作者: staceyfff 时间: 2011-10-27 23:12
谢谢LZ~作者: bbfcsak 时间: 2011-10-27 23:39
感谢~选B作者: tinahuang95 时间: 2011-10-28 00:31
