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  3. Drugs can be divided into three main groups: those that a person can buy without a prescription. those that a person needs a doc

Drugs can be divided into three main groups: those that a person can buy without a prescription. those that a person needs a doc

admin2010-07-24  22
问题     Drugs can be divided into three main groups: those that a person can buy without a prescription. those that a person needs a doctor’s prescription for, and those that are illegal.
    Two popular nonprescription drugs are caffeine (咖啡因) and alcohol. Caffeine is found in coffee, tea, chocolate, and cola drinks. It is a mental stimulant; it stimulates the central nervous system and makes people feel alert. Students, for example, often find they can study better if they have a cup of coffee. On the other hand, caffeine can also make people nervous and irritable. If people drink too much caffeine, they may have trouble sleeping.
    Alcohol is a depressant; it depresses the central nervous system. When people drink, they have less control over their actions. They cannot walk in a straight line and they cannot drive as well as when they are alcohol-free in their blood. People who drink a great deal sometimes fall into a deep sleep. Later, they may wake up with a strong headache.
    In addition to these nonprescription drugs, there are two major categories of prescription drugs : stimulants and depressants. The depressants include morphine(吗啡), which is used as a pain killer. The most common stimulants are amphetamines (苯丙胺). Doctors used to prescribe amphetamines as diet pills ; however, they found that amphetamines can have serious side effects. They can make a patient very nervous, and when the drug wears off, the patient may feel very depressed. Doctors still give amphetamines to people with narcolepsy, an illness that causes sudden, uncontrollable attacks of sleep.
    The largest class of illegal drugs are hallucinogens, drugs that .change the way a person thinks and cause hallucinations, or visions. For some people, marijuana(大麻) is a mild hallucinogen. Marijuana generally brings a pleasant feeling. However, when people smoke marijuana, they sometimes can not concentrate very well on their activities, such as their work or driving.
Mention the different functions of caffeine and alcohol.
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答案Caffeine stimulates nervous system while alcohol depresses it. 或One stimulates and the other depresses nervous system
解析 这句问题要求我们比较两者之间的不同。回答这类问题往往不是三言两语能说清楚的。我们要抓住最根本的来回答，千万别把原文整句整句地当答案抄。写得再好的答案如果过长，很可能会引起阅卷人的反感。在此，我们把nervous system作两个动词的宾语既省字数，也让人一看就明白。
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