Only three strategies are available for controlling cancer: prevention, screening and treatment. Lung cancer causes more deaths than any other types of cancer. A major cause of the disease is not 【21】______ known there is no 【22】______ evidence that screening is much help and treatment 【23】______ in about 90 percent of all cases. At present, therefore, the main strategy must be 【24】______ . This may not always be true, of course, as for some other types of cancer, research 【25】______ the past few decades has suggested some importance in prevention, screening or treatment. 【26】______ , however, we consider not what research may one day offer but what today’s knowledge could already deliver that is not being delivered, then the most practicable and cost-effective opportunities for 【27】______ premature death from cancer, especially lung cancer, probably involve neither screening nor improved treatment, 【28】______ prevention. This conclusion does not depend on the unrealistic assumption that we can 【29】______ tobacco. It merely assumes that we can reduce cigarette sales appreciably by raising prices or by 【30】______ on the type of education that already appears to have a 【31】______ effect 【32】______ cigarette assumption by white-collar workers and that we can substantially reduce the amount of tar 【33】______ per cigarette. The practicability of preventing cancer by such measures applies not only in those countries, such as, the United States of America, because cigarette smoking has been common for decades, 25 to 30 percent of all cancer deaths now involves lung cancer, but also in those where it has become 【34】______ only recently. China is a good example. Countries where cigarette smoking is only becoming widespread can expect enormous increase in lung cancer during the 1990’s or early in the next century, 【35】______ prompt effective action is taken 【36】______ the habit. There are three reasons 【37】______ the prevention of lung cancer is of such overwhelming importance: first, the disease is extremely common, causing more deaths than any other type of cancer now 【38】______ secondly, it is generally incurable and finally, 【39】______ tobacco consumption will also have a substantial 【40】______ on many other diseases. 【21】