听力原文：Until the twentieth century cigarettes were not an important threat to public hea

听力原文： Until the twentieth century cigarettes were not an important threat to public health. Since the cigarette industry began in the 1870s, however cigarette manufacturing machines have developed rapidly. This made it possible to produce great numbers of cigarettes very quickly, and it reduced the price.

Today cigarette smoking is a widespread habit. About forty-three percent of the men and thirty-one percent of the adult women in the United States smoke cigarette regularly. It is encouraging to note, however, that millions of people have been giving up the smoking habit.

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 income are less likely to smoke cigarette than men with fewer years of schooling and lower incomes. On the other hand, if a well- educated man with a high income smokes at all, he is likely to smoke more packs of cigarettes per day. The situation is somewhat different for women. There are slightly more smokers among women with higher family income and higher education than among the lower income and lower educational groups. These more highly educated women tend to smoke more heavily.

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A．The increasing output of tobacco.

B．The rapid development of cigarette-making machine.

C．The rapid development of cigarette-making factories.

D．The great number of people engaged in cigarette producing.