根据材料请回答 16～22 Smoking Since 1939, numerous studies have been conducted to determine whether smoking is a health hazard.The trend of the evidence has been consistent and indicates that there is a serious health risk.Research teams have conducted studies that show beyond all reasona-ble doubt that tobacco smoking is associated with a shortened life expectancy (预期寿命). Cigarette smoking is believed by most research workers in this field to be an important factor in the development of cancer of the lungs and cancer of the throat and is believed to be related to cancer of some other organs of the body.Male cigarette smokers have higher death rate from heart disease than none-smoking males.Female cigarette smokers are thought to be less affected because they do not breathe in the smoke so deeply. Apart from statistics, it might be helpful to look at what smoking tobacco does to the human body.Smoke is a mixture of gases, vaporized chemicals, minute particles of ash and other solids.There is also nicotine (尼古丁), which is powerful poison, and black tar.As smoke is breathed in, all those components form. deposits on the membranes (膜) of the lungs.One point of concentration is where the air tube and bronchus divides.Most lung cancer begins at this point. Filters (过滤嘴) and low tar tobacco are claimed to make smoking to some extent sa-fer, but they can only slightly reduce, not eliminate, the hazards. 第 16 题 It is easy to determine whether smoking is hazardous.