单项选择题

Can exercise be a bad thing Sudden death during or soon after strenuous exertion on the squash court or on the army training grounds, is not unheard of. (1) trained marathon runners are not immune to fatal heart attacks. But no one knows just (2) common these sudden deaths linked to exercise are. The registration and investigation of such (3) is very patchy; only a national survey could determine the true (4) of sudden deaths in sports. But the climate of medical opinion is shifting in (5) of exercise, for the person recovering from a heart attack as (6) as the average lazy individual. Training can help the victim of a heart attack by lowering the (7) of oxygen the heart needs at any given level of work (8) the patient can do more before reaching the point where chest pains indicate a heart starved of oxygen. The question is, should middle-aged people, (9) particular, be screened for signs of heart disease before (10) vigorous exercise

（10）处填（）

点击查看答案&解析