A the incidence of mesothelioma is extremely low B which may extend from 25 to 30 year after initial exposure C whereas the latter consist of a collection of fluid in the chest region outside the lungs D on the other hand, are exclusively associated with exposure to the less harmful white asbestos E suspect that exposure to even minimal levels of asbestos is unacceptable F causing scarring which limits the functioning of the lungs G resulting from inadequate ventilation H develop the barrel-shaped chests associated with emphysema 肺气肿(where the skin assumes a bluish color) and club fingers The inhalation of asbestos particles is associated with a number of lung diseases, such as asbestosis and lung cancer. Asbestosis is caused by the entry of asbestos particles into the walls of the alveoli, 【B1】______ . The lung loses its elasticity and may change shape. The initial symptoms of asbestosis are a tightness in the chest and breathlessness. In its later stages, sufferers 【B2】______ . Lung cancer, the genetic term for malignant tumors of the alveoli and bronchial tubes, has been shown to be directly related to the inhalation of asbestos particles. As in the case of asbestosis, there is generally a period of latency 【B3】______ , despite the absence of further exposure. Research suggests that there is a direct correlation between the degree of exposure to asbestos and the incidence of lung cancers. Where exposure occurs, the level of risk is further increased by cigarette smoking. Asbestos workers who smoke cigarettes have a 90% greater risks of contracting lung cancer than workers who do not smoke. 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 【B4】______ . Where epidemiological surveys have revealed a higher incidence of the disease, it is almost always related to asbestos exposure. 【B1】______