原文：Until the twentieth century cigarettes were not an important threat to public health. Men used tobacco mainly in the form of cigars. They chewed tobacco, piped tobacco, and snuffed. Most women did not use tobacco at all.The cigarette industry began in 1870s with the development of the cigarette manufacturing machine. 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 adult men and thirty-one percent of the adult women in the United States smoke cigarettes regularly. It is encouraging to note, however, that millions of people have quit smoking. Seventy-five percent of the male population and forty-six percent of the female population have smoked cigarettes for some time during their lives, but twenty-six percent of these men and eleven percent of the women have stopped smoking. The number of persons who have given up smoking is increasing. Men as a group smoke more than women. Among both men and women the age group with the highest proportion of smokers is the age group 24—44.Income, education, and occupation all play a part in determining a person’s smoking habit. 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, he’s 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 incomes and higher education than among the lower income and lower educational groups. These more highly educated women tend to smoke more heavily.Among teenagers the picture is similar. There are fewer teenager smokers from upper-income, well-educated families, and also fewer from families living in farm areas. High school students who are preparing for college are less likely to smoke than those who don’t plan to continue their education after high school. Children are most likely to start smoking if one or both of their parents smoke.
题目（纸质上非本人所做，不是全对）：
答案分析：
选B
第一问应该在第一段 注意是[importantthreat] to 而不是thread to
第三问也印证了这点。也只是说 是成为一个威胁，因此全文只有第一句提到这个。
第一句not until句型 直到20世纪 香烟才是一个对公共健康的重大的威胁。
因此题目是became 这样的话应该选D 直到20世纪才成为威胁
D项 Since应该和过去完成时搭配而题目是became一般过去时 时态不对。
而且直到20世纪 并没说是20世纪初还是中期。
选B
A 第一段没有说历史原因因此不对
C 只是介绍现象并没有解释原因 因此不对
D 文中是most并不是no程度限定不对
结合第二段
C
第二段 讲的是第三题的内容
第三段是today怎么样 讲另外一回事。
香烟生产机器的提高 怎样对公共健康产生威胁。答案在下面的那句话。显然是因为生产的更快，价格还便宜。因此选C“用低廉的成本就可以造大量的香烟制品”
上一段说 吸烟人群 男性比女性多，最重要的是 工资教育水平高的反而吸烟少。
A虽然没在这段出现但是在前面出现。为什么成为威胁 因为制烟技术的发展，廉价。
因此低收入 低层次的人才有机会形成现在的“吸烟习惯”显然A也是一个因素。
首先文中没有提D （香烟上的图片，是影响因素） 。B和C明确说 显然正确
因此选D
选B 文章说女性和男性的情况不同。女性教育好的反而吸烟会略高一点。
D对应最后一句
C对应第一句 city children显然属于city people。A对应第二句
