The judgment that cigarette smoking is (36) to health is the result of more than 30 years of research carried on by hundreds of scientists in this country and abroad. The (37) that cigarette smoking is a significant health hazard is supported by every medical and health (38) in the world which is known to have (39) an opinion on the matter. While cigarette smokers tend to have higher death rates than nonsmokers, 80 percent of the excess deaths (40) with this habit are caused by three ’major diseases. They are lung cancer, (41) heart disease, and emphysema. Lung cancer was a rare disease 50 years ago. Today, it is (42) that 60,000 men and women per year in the United States will die of this disease. Among men it is the most (43) cause of death from cancer. Cigarette smoking is the major cause of lung cancer. (44) , they are of small importance compared with cigarette smoking. (45) . Approximately 90 percent of all primary cancer cases occur in people who smoke cigarettes. Laboratory studies have isolated from tobacco smoke a number of chemical compounds that can cause caner. (46)

坡屋顶一般由（）等基本层次组成。

A.屋面

B.保温层

C.顶棚

D.找平层

E.承重结构