以下贴的是我的OG-1文章的阅读笔记，做第6题时，虽选了B，但是觉得A,E也有道理。后来做阅读笔记时，写下了E不成立的理由，但不知是否成立？请参看我的阅读笔记并帮助我解释一下第六题。谢谢！

“the most widely used psychoactive substance on Earth .”

Synder, Daly and Bruns have recently proposed that

caffeine affects behavior by countering the activity in 底二题的逻辑推理关系：

(5) the human brain of a naturally occurring chemical called C up—ad down

adenosine. Adenosine normally depresses neuron firing ad up—nf down

in many areas of the brain. It apparently does this by ---ad up—nf down—ne down

inhibiting the release of neurotransmitters, chemicals ---c up---nf up---ne up

that carry nerve impulses from one neuron to the next.

(10) Like many other agents that affect neuron firing,

adenosine must first bind to specific receptors on

neuronal membranes. There are at least two classes

of these receptors, which have been designated A1 and

A2. Snyder et al propose that caffeine, which is struc-

(15) turally similar to adenosine, is able to bind to both types

of receptors, which prevents adenosine from attaching

there and allows the neurons to fire more readily than

they otherwise would.

For many years, caffeine’s effects have been attri- 老观点及S的反对

(20) buted to its inhibition of the production of phosphodi-

esterase, an enzyme that breaks down the chemical

called cyclic AMP.A number of neurotransmitters exert

their effects by first increasing cyclic AMP concentra-

tions in target neurons. Therefore, prolonged periods at

(25) the elevated concentrations, as might be brought about

by a phosphodiesterase inhibitor, could lead to a greater

amount of neuron firing and, consequently, to behav-

ioral stimulation. But Snyder et al point out that the

caffeine concentrations needed to inhibit the production

(30) of phosphodiesterase in the brain are much higher than

those that produce stimulation. Moreover, other com-

pounds that block phosphodiesterase’s activity are not

stimulants.

To buttress their case that caffeine acts instead by pre- S用实验验证新观点

(35) venting adenosine binding, Snyder et al compared the

stimulatory effects of a series of caffeine derivatives with

their ability to dislodge adenosine from its receptors in

the brains of mice. “In general,” they reported, “the

ability of the compounds to compete at the receptors

(40) correlates with their ability to stimulate locomotion in

the mouse; i.e., the higher their capacity to bind at the

receptors, the higher their ability to stimulate locomo- 比较级要予以关注

tion.” Theophylline, a close structural relative of caffeine

and the major stimulant in tea, was one of the most

(45) effective compounds in both regards.

There were some apparent exceptions to the general 延伸新内容—不成为主题内容

correlation observed between adenosine-receptor binding

and stimulation. One of these was a compound called

3-isobuty1-1-methylxanthine(IBMX), which bound very

(50) well but actually depressed mouse locomotion. Snyder

et al suggest that this is not a major stumbling block to

their hypothesis. The problem is that the compound has

mixed effects in the brain, a not unusual occurrence with

psychoactive drugs. Even caffeine, which is generally

(55) known only for its stimulatory effects, displays this

property, depressing mouse locomotion at very low

concentrations and stimulating it at higher ones.

1. The primary purpose of the passage is to Main idea—新老观点套路

(A) discuss a plan for investigation of a phenomenon that is not yet fully understood-incorrective

(B) present two explanations of a phenomenon and reconcile the differences between them—support S’s view not reconcile them

(C) summarize two theories and suggest a third theory that overcomes the problems encountered in the first two—not mention

(D) describe an alternative hypothesis and provide evidence and arguments that support it—1P is new view by S, 2P is old view and 3p to buttress new view, 4P is a exception

(E) challenge the validity of a theory by exposing the inconsistencies and contradictions in it-not only challenge but also focus on new position

2. According so Snyder et al, caffeine differs from adenosine in that caffeine L4-8 and L14-18,须推出逻辑关系，费时间

(A) stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans only

(B) has mixed effects in the brain, whereas adenosine has only a stimulatory effect

(C) increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrations

(D) permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such release c(up)—ad(down)--ne (up); ad(up)—nf (down)—ne(down)

(E) inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firing

3. In response to experimental results concerning IBMX, Snyder et al contended that it is not uncommon for psychoactive drugs to have --定位词—L53, 4P—同义变换—unusual

(A) mixed effects in the brain

(B) inhibitory effects on enzymes in the brain—2p

(C) close structural relationships with caffeine---ad

(D) depressive effects on mouse locomotion---comparative relationship

(E) the ability to dislodge caffeine from receptors in the brain—3p, L37

4. According to Snyder et al, all of the following compounds can bind to specific receptors in the brain EXCEPT—定位+排除

(A) IBMX

(B) caffeine

(C) adenosine

(D) theophylline

(E) phosphodiesterase

5. Snyder et al suggest that caffeine’s ability to bind to A1 and A2 receptors can be at least partially attributed to which of the following? 定位词—1P—L15—同义变换

(A) The chemical relationship between caffeine and phosphodiesterase

(B) The structural relationship between caffeine and adenosine

(C) The structural similarity between caffeine and neurotransmitters

(D) The ability of caffeine to stimulate behavior

(E) The natural occurrence of caffeine and adenosine in the brain

6. The author quotes Snyder et al in lines 38-43 most probably in order to---3段句首有词to buttress, so I think there is 2 possibilities, one is to refute old theory, another is to support S’s new view. If that, A,B and E are my consideration for this subject.

(A) reveal some of the assumptions underlying their theory？

(B) summarize a major finding of their experiments---引出S的话，是为了总结S的实验发现和证明S的假设理论

(C) point out that their experiments were limited to the mouse

(D) indicate that their experiments resulted only in general correlations

(E) refute the objections made by supporters of the older theory-文章提出就理论时，是以一种理论感念提出，并未说该理论的支持者反对S的理论。