第5部分：補(bǔ)全短文(第46?50題，每題2分，共10分)

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Lung Cancer

The death rate due to cancer of the lungs has increased more than 800 percent in males and has more than doubled in females during the last 25 years. (46) There are many possible causes, but it is still controversial which are most blameworthy. Those factors which have been mentioned most frequently are the presence of foreign particles and other irritants in the air (smoke particles, smog, exhaust fumes), and the smoking of cigarettes and cigars.

(47) Among heavy smokers ^21 to 30 cigarettes per day ^the mortality rate from lung cancer is nearly 17 times the rate from nonsmokers. It is expected the death rate among women will increase as the present high rate of smoking among women has its effect.

Sometimes cases of lung cancer are discovered at the time an x-ray is taken for the purpose of detecting tuberculosis. Too often, however, a current emphasis upon the danger of exposure to radiation 1 from X-ray machines can frighten people away from routine chest X-rays and thus prevent an early diagnosis of lung cancer.

(48) Modem X-ray machines in competent hands pose such slight danger,

at least to those over 40 years of age, that this would be much more than offset by the advantages of discovering a tumor while it is small enough to be completely removed.3

(49) The tumor may grow until the bronchus is blocked, cutting off6 the supply of air to that

lung. The lung then collapses, and the secretions trapped in the lung spaces become infected, with a resulting pneumonia or the formation of a lung abscess. Such a lung cancer can also spread to cause secondary growths in the lymph nodes7 of the chest and neck as well as in the brain and other parts of the body. The only treatment that offers a possibility of cure, before secondary growths have had time to form, is to remove the lung completely. (50)

Malignant tumors of the stomach, the breast, the prostate gland8 and other organs may spread to the lungs, causing secondary growths.

A. This operation is called pneumonectomy.

B. It is considerably higher in urban and industrial areas than in rural districts.

C. Routine X-ray chest examination is not dangerous.

A. Numerous studies have demonstrated a striking correlation between the death rate from lung cancer and smoking habits.

B. Early detection is absolutely essential if any possibility of cure is to be maintained.

C. A common form of lung cancer is bronchogenic carcinoma4，so-called because the malignancy originates in5 a bronchus.

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