题目内容：
根据下面资料，回答题 Walking--like swimming, Bicycling and running-is an aerobic exercise, (31) _____builds the capacityfor energy output and physical endurance by increasing the supply of oxygen to skin and muscles. Such exercisesmay be a primary factor in the (32)_____of heart and circulatory disease.
As probably the least strenuous, safest aerobic activity, walking is the (33) _____acceptable exercise forthe largest number of people. Walking (34)_____ comfortable speed improves the efficiency of the cardiorespi-ratory system (35)_____ stimulating the lungs and heart, But at a more gradual rate (36)_____ most otherforms of exercise.
In one test, a group of men 40 to 57 years of age, (37)_____ at a fast pace for 40 minutes four days aweek, showed improvement (38)_____ to men the same age on a 30 minute, three-day-a-week jogging programin the same period. Their resting heart rate and body fat decreased (39)_____ These changes suggest(40)_____ of the important---even vital--benefits walking can (41)_____ about.
Walking (42) _____ burns calories. It takes 3,500 calories to gain or (43)_____ one pound. Since aone-hour walk at a moderate pace will (44)_____ up 300 to 360 calories. By walking one hour every other day,you can burn up a pound-and-a-half monthly, or 18 pounds (45)_____ --providing there is no change in your in-take of food. To (46)_____weight faster, walk an hour every day and burn up 3 pounds a month, or 36 poundsa year.
(47)_____ your age, fight now is the time to give your physical well-being as much thought as you(48)_____ to pensions or insurance. Walking is a vital defense (49) _____ the ravages of degenerative diseasesand aging. It is nature's (50) _____ of giving you a tuneup.
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