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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

admin2010-09-10  120
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.
What is the meaning of "alcohol-free" ?
选项
答案Without alcohol or no alcohol
解析 就文章词或短语的同义提问，我们在前面已经见过。做这类题需要分两步布骤：首先确定词义，从生词前后，甚至整段中归纳出答案来。其次，正确地解释词义。解释词义往往比确定词义要困难。因为不少考生对问义的理解往往是心里明白，但说不出来，或者说不能用精练的语言说出来。
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