阅读下面的短文，并根据所读内容在文章后表格中的空格里填入最恰当的单词。
注意：每空一词。
The health dangers of smoking have been well reported. For years, doctors have warned that smoking can cause lung cancer. Studies also have linked smoking to several other kinds of cancer, heart attacks and other diseases, lung diseases, and a number of other medical problems. The repeated health warnings have had an effect. Thousands of people have stopped smoking. But as many people have learned, stopping smoking can be very difficult.
A major problem apparently is the nicotine, a poisonous substance found in tobacco. Small amounts of nicotine are released as tobacco is burned. And over many years of smoking, a person’s body becomes dependent on the substance. An attempt to stop smoking brings the problems of nicotine withdrawal (脱瘾过程).
American medical researchers have found that nicotine withdrawal causes people to become angry very easily, aggressive, worried and unable to think sharply. Many people who have tried to stop smoking would
