Passage 2Italians smoke seven thousand million cigarettes every year (1987 figures). This is roughly the equivalent of 5,195 cigarettes a year for every person in the country of 20 years of age or more. It is estimated that 55% of Italian men smoke compared with 38% of Italian women. Since 1939, numerous scientific studies have been carried out to determine whether smoking is a health hazard. The findings show that tobacco smoking, particularly cigarette smoking is associated with a shortened life expectancy（寿命）. Cigarette smoking is believed by most research workers to be an important factor in the development of cancer of the lungs and cancer of the throat. Male cigarette smokers have a higher death rate from heart disease than nonsmoking males. (Female smokers are thought to be less affected because they do not breathe in the smoke so deeply.) The majority of physicians and researchers say：“Give up smoking .If you don’ t smoke—don’t start!” Some competent physicians and research workers though their small number is dwindling even further－are less sure of the effect of cigarette smoking on health. They consider the increase in respiratory diseases （呼吸道疾病）and various forms of cancer may possibly be explained by other factors in the complex human environment atmospheric pollution, increased nervous stress, chemical substances in processed food, or chemical pesticides that are now being used by farmers in vast quantities to destroy insects and small animals. Smokers who develop cancer or lung diseases, they say, may also, by coincidence, live in industrial areas, or eat more canned food. Smoke is a mixture of gases, vaporized chemicals, minute particles of ash, and other solids. There is also nicotine, which is a powerful poison, and black tar .As the smoke is breathed in, all these components form deposits（沉积物）on the membranes（膜）of the lungs .While all tobacco smoking affects life expectancy and health, cigarette smoking appears to have a much greater effect than cigar or pipe smoking. However, nicotine consumption is not diminished by the latter forms, and current research indicates a causal relationship between all forms of smoking and cancer of the mouth and throat. Filters （过滤嘴）and low tar tobacco are claimed to make smoking to some extent safer, but they can only marginally reduce, not eliminate the hazards.8. Smoke is a mixture of components, except______.