A、Because machines reduced the price and made cigarettes popular. B、Because cigarette industry only began to develop in the 1870

Until the 20th century cigarette smoking was not a widespread habit. The cigarette industry started in the 1870’s with the development of cigarette manufacturing machines. It helped produce great numbers of cigarettes very quickly and reduced the price greatly. And consequently more and more people, both men and women, began to smoke cigarettes. Men as a group, however, smoke more than women. But the highest proportion of smokers is found in the age group of 24-44, regardless of sex difference. Income, education, and occupation all play a part in determining a person’s smoking habits. City people smoke more than people living on farms. Well-educated men with high incomes are less likely to smoke cigarettes than men with fewer years of schooling and lower incomes. On the other hand, if a well-educated man with a higher income smokes at all, he is likely to smoke more packs of cigarettes per day. The situation is somewhat different from woman. There are slightly more smokers among women with higher family incomes and higher education than among the lower income and lower education groups. These more highly educated women tend to smoke more heavily. Among teenagers the picture is similar. There are fewer teenage smokers from upper-income, well-educated families, and fewer from families living in farm areas. High school students who are preparing for college are less likely to smoke than those who do not plan to continue their education after high school. Children are most likely to start smoking if one or both of their parents smoke.
16. Why did smoking become widespread in the 20th century?
17. Which age group of people takes up the highest proportion among the smokers?
18. Which group of teenagers is most likely to smoke according to the passage?