听力原文： Why do people smoke? One reason is that people become dependent on cigarettes. The substance which people cannot resist in cigarettes is nicotine. when people smoke the nicotine goes directly into the blood stream and makes people feel relaxed. A smoker's body gets accustomed to the nicotine and if he stops smoking he feels nervous. Many smokers try to stop smoking but because of their dependence on nicotine they feel so uncomfortable that they often find it too hard to stop. Another reason is that people simply enjoy smoking and what it symbolizes. Having a cigarette for many people means taking a break. For some people smoking becomes part of certain social forms, for example, the cigarette after dinner. Many people enjoy smoking because it makes their hands busy. Many people also like the taste of tar in cigarettes. However, it is the tar that causes cancer. While governments and health experts have tried to make people give up smoking entirely, cigarette manufacturers have to keep selling them by producing cigarettes with less tar. Many people in western countries have welcomed these cigarettes since they find it difficult to stop smoking but want to reduce the risk to their health. Why do so many people become dependent on cigarettes?