首字母提炼 套路词汇 重点词汇 可能的考点（要引起高度重视的内容，可能会有考点的出现） Caffeine, the stimulant in coffee, has been called “the most widely used psychoactive substance on Earth .” Synder, Daly and Bruns have recently（说明是新观点，则后面可能有老观点出现） proposed that caffeine affects behavior by countering the activity in (5) the human brain of a naturally occurring chemical called adenosine.（提出观点） Adenosine normally depresses neuron firing in many areas of the brain. It apparently does this by inhibiting the release of neurotransmitters,（后面解释ne） chemicals that carry nerve impulses from one neuron to the next. (10) Like many other agents（注意出现比较） 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, （出现比较）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. （第一段看完，总结一下出现了ca， ad， neu等物质，还有sy等人， 提出了一个新观点） For many years,（说明出现老观点） caffeine’s effects have been attri- (20) buted to its inhibition of the production of phosphodi- esterase,（解释ph是什么东西） 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. （老观点，看不懂没有关系，注意一些关键字，以及therefore后面的总结点，等到后面有问题再回来定位。）But（一定要注意，出现转折） 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.（只需要记得sny对老观点进行了反驳，具体内容晦涩，不懂没有关系） （提出老观点，同时指出sny对老观点有反驳） To buttress their case that caffeine acts instead by（注意不是instead of， 因此后面的是新观点的总结） pre- (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,”（出现引号，注意） 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- tion.” Theophylline, a close structural relative（比较） 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 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. （后面有解释，看清楚）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. （sny利用试验等证明了假设，同时指出了一个问题，但是又解决了这个问题） 1. The primary purpose of the passage is to (A) discuss a plan for investigation of a phenomenon that is not yet fully understood (B)present two explanations of a phenomenon and reconcile the differences between them (C) summarize two theories and suggest a third theory that overcomes the problems encountered in the first two (D) describe an alternative hypothesis and provide evidence and arguments that support it（D） (E) challenge the validity of a theory by exposing the inconsistencies and contradictions in it （本文中提出的是假设，注意用词，同时只有d符合文章的内容） 2. According so Snyder et al, caffeine differs from adenosine in that caffeine (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（D） (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 1，caffeine与ad的比较定位在第一段，可以找到答案，此外，也可以 进行无关词的排除，即不是第一段的词排除，确认答案。 3. In response to experimental results concerning IBMX, Snyder et al contended that it is not uncommon（就是common，要找出psyo的普遍特性） for psychoactive drugs to have (A) mixed effects in the brain (B)inhibitory effects on enzymes in the brain (C) close structural relationships with caffeine (D) depressive effects on mouse locomotion（A） (E) the ability to dislodge caffeine from receptors in the brain ibmx定位在最后一段， 4. According to Snyder et al, all of the following compounds can bind to specific receptors in the brain EXCEPT（利用首字母的定位，找到定义，同时也可以注意到 ph是在第二段里没有提到连接的问题，连接是新观点，也可以排除） (A) IBMX (B)caffeine (C) adenosine (D) theophylline（E） (E) phosphodiesterase 5. Snyder et al suggest that caffeine’s ability to bind to A1 and A2（定位第一段） receptors can be at least partially attributed to which of the following? (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（B） (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 (A) reveal some of the assumptions underlying their theory (B)summarize a major finding of their experiments (C) point out that their experiments were limited to the mouse (D) indicate that their experiments resulted only in general correlations（B） (E) refute the objections made by supporters of the older theory 小节，没有考一些很复杂的过程，考的内容较为基本。1. D is the best answer. 不知道为什么显示不出颜色，我上传word文档吧。 这是第一篇，大家可以尝试自己按照这样的方法做做题，不要求速度，先培养感觉。
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，然后选择里面的颜色，确定就可以了。