请问小安阅读中里这道阅读题是怎么选出来的？

celiauuuuu

文章：

Caffeine, thestimulant in coffee, has been called “the most widely used psychoactive精神活性物质 substance onEarth.” Snyder, Daly and Bruns have recently proposed that caffeine affectbehavior by countering the activity in the human brain of a naturally occurringchemical called adenosine. Adenosine normally depresses neuron firing in manyareas of the brain. It apparently does this by inhibiting the release ofneurotransmitters, chemicals that carry nerve impulses from one neuron to thenext. Like many other agents that affect neuron firing, adenosine must firstbind to specific receptors on neuronal membranes. There are at least twoclasses of these receptors, which have been designated A1 and A2.Snyder et al (et al: abbr. (Lat) 以及其他人，等人) propose that caffeine, which is structurallysimilar to adenosine,is able to bind to both types of receptors, which prevents adenosinefrom attaching there and allows the neurons to fire more readily than theyotherwise would.提出新的Snyder的发现

旧观点For many years,caffeine’s effects have been attributed to its inhibition of the production ofphosphodiesterase, an enzyme that breaks down the chemical called cyclic AMP. Anumber of neurotransmitters exert their effects by first increasing cyclic AMPconcentrations intarget neurons. Therefore, prolonged periods at the elevated concentrations, asmight be brought about by a phosphodiesterase inhibitor, could lead to agreater amount of neuron firing and, consequently, to behavioral stimulation.But 强转折Snyderet al point out that the caffeine concentrations needed to inhibit theproduction of phosphodiesterase in the brain are much higher than those thatproduce stimulation. Moreover, other compounds that block phosphodiesterase’sactivity are not stimulants.

To buttress their case that caffeine actsinstead by preventing adenosine binding, Snyder et al compared the stimulatoryeffects of a series of caffeine derivatives with their ability to dislodgeadenosine from its receptors in the brains of mice. “In general,” they reported, “the ability ofthe compounds to compete at the receptors correlates with their ability tostimulate locomotion in the mouse; i.e., the higher their capacity to bind atthe receptors, the higher their ability to stimulate locomotion.” Theophylline,a close structural relative of caffeine and the major stimulant in tea, wasone of the most effective compounds in both regards.

There were some apparent exceptions to thegeneral correlation observed between adenosine-receptor binding andstimulation. One of these was a compound called 3-isobutyl-1-methylxanthine (IBMX),which bound very well but actually depressed mouse locomotion. Snyder et alsuggests that this is not a major stumbling block (stumbling block: n.障碍物, 绊脚石) to their hypothesis. Theproblem is that thecompound has mixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Evencaffeine, which is generally known only for its stimulatory effects, displaysthis property, depressing mouse locomotion at very low concentrations andstimulating it at higher ones.

这两题做错了，请大牛帮忙讲解一下，万分感谢：

Whichof the following, if true, would most weaken the theory proposed by Snyder etal? 还是不是很明白D为何正确。。。

(A) At very low concentrations in the humanbrain, both caffeine and theophylline tend to have depressive rather thanstimulatory effects on human behavior.

(B) The ability of caffeine derivatives atvery low concentrations to dislodge adenosine from its receptors in mousebrains correlates well with their ability to stimulate mouse locomotion atthese low concentrations.

(C) The concentration of cyclic AMP intarget neurons in the human brain that leads to increased neuron firing can beproduced by several different phosphodiesterase inhibitors in addition to caffeine.

(D) The concentration of caffeine required to dislodge adenosine from itsreceptors in the human brain is much greater than the concentration thatproduces behavioral stimulation in humans. 是因为最后一句吗？ D正确

(E) The concentration of IBMX required todislodge adenosine from its receptors in mouse brains is much smaller than theconcentration that stimulates locomotion in the mouse.

Theauthor quotes Snyder et al in lines 16-18 most probably in order to   line16-18就是P3 To buttress那一句 文字是紫色的

(A) reveal some of the assumptionsunderlying their theory      

(B) summarize a major finding of their experiments=ingeneral的同义改写，in order to 的题在总结句里找

(C) point out that their experiments werelimited to the mouse   

(D) indicate that their experimentsresulted only in general correlations（B）

(E) refute the objections made bysupporters of the older theory 证明他们自己的观点是对的，而不是反对其他人的观点吗？

这道题我选的是E，为什么E错呀？正确的是B