单选题：阅读下文，回答题。SMOKING1 Since 1939，numerous studies have been con

阅读下文，回答题。
SMOKING
1 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 reasonable doubt that tobacco smoking is associated with a shortened life expectancy.
2 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 a higher death rate from heart disease than non-smoking males. Female smokers are thought to be less affected because they do not breathe in the .smoke so deeply.
3 Apart from statistics, it might be helpful to look at what 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，which is powerful poison, and black tar. One point of concentration is where the air tube and bronchus divides. Most lung cancer begins at this point
4 Filters and low tar tobacco too are claimed to make smoking to some extent safer, but they can only slightly reduce，not eliminate the hazards.
It is easy to determine whether smoking is hazardous. A．Right
B．Wrong
C．Not mentioned