As in the case of asbestosis, there is generally a period of inactiveness which may ___56___ from 25 to 30 years after initial exposure, despite the ___57___of further exposure.

　　Research suggests that there is a direct correlation between the degree of exposure to asbestos ___58___the incidence of lung cancer.

　　Where exposure occurs, the level of risk is further ___59___ by cigarette smoking.

　　Asbestos workers who smoke cigarettes have a 90% greater risk of catching lung cancer than workers who do not ___60___.

　　Exposure to blue asbestos has been shown to produce mesothelioma, a rare cancer of the outer lining of the lung or pleura.

　　In a normal population the incidence of mesothelioma is extremely ___61___. Where epidemiological surveys have revealed a higher incidence of the disease, it is almost always related to ___62___ exposure.

　　___63___ changes in lung tissue caused by exposure to asbestos are pleural plaques and effusions.

　　The former refer to a thickening of the lining of the chest wall, ___64___ the latter consists of a collection of fluid in the chest region outside the lungs.

　　Pleural plaques commonly remain undiagnosed and generally have no detrimental effect on health.

　　41．A. skin

　　B. blood

　　C. liver

　　D. lung

　　42．A. loses

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