2002北航考博英语真题阅读理解及其答案.pdf

中国考博辅导首选学校 2002北航考博英语真题阅读理解及其答案 Technically, any substance other than food that alters our bodily or mental functioning is a drug. Many people mistakenly believe the term drugrefers only to some sortofmedicine or an illegalchemical taken by drug addicts. They dont realize that familiar substances such as alcohol and tobacco are also drugs. This is why the more neutral term substance is now used by many physicians and psychologists. The phrase substance abuse is often used instead of drug abuse tomake clear that substances such as alcohol and tobacco can be just as harmfully misused as heroin and cocaine. We live in a society in which the medicinal and social use of substances (drugs)ispervasive: anaspirin toquietaheadache, some wine to be sociable, coffee to get going in the morning, a cigarette for the nerves. When do these socially acceptable and apparently constructive uses of a substance become misuses? First of all, most substances taken in excess will produce negative effects such as poisoning or intense perceptual distortions. Repeated use of a substancecanalso leadtophysicaladdictionorsubstancedependence. Dependence ismarked first by an increased tolerance, with more and moreofthesubstancerequiredtoproducethedesiredeffect,andthen by the appearance of unpleasant withdrawal symptoms when the substance is discontinued. Drugs (substances) that affect the central nervous system and alter perception, mood, and behavior are known as psychoactive 中国考博辅导首选学校 substances. Psychoactive substances are commonly grouped according to whether they are stimulants, depressants, or hallucinogens. Stimulants initiallyspeeduporactivatethecentralnervous system, whereas depressants slow it down. Hallucinogens have their primary effectonperception, distortingand altering it inavariety ofways including producing hallucinations. These are th