The judgment that cigarette smoking is【B1】______ to health is the result of

The judgment that cigarette smoking is (36) hazardous 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) conclusion that cigarette smoking is a significant health hazard is supported by every medical and health (38) agency in the world which is known to have (39) expressed an opinion on the matter.
    While cigarette smokers tend to have higher death rates than nonsmokers, 80 percent of the excess deaths (40) associated with this habit are caused by three major diseases. They tree lung cancer, (41) coronary heart disease, and emphysema. Lung cancer was a rare disease 50 years ago. Today, it is (42) estimated that 60,000 men and women per year in the United States will die of this disease Among men it is the most (43)common cause of death from cancer.
    Cigarette smoking is the major cause of lung cancer. (44) Although chronic irritation from certain chemical substances, radiation, viruses, occupational hazards, air pollution, and other environmental factors have been implicated in this disease, they are of small importance compared with cigarette smoking. (45) To those who smoke, however, they can be important in increasing the risks still further. 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) In addition, there are elements in smoke that interact with other compounds to promote cancer production.