单选题 Fifty volunteers were alphabetically divided into two equal groups, Group A to participate (91) a 7-week exercise program, and Group B to avoid (92) exercise of any sort during those 7 weeks. On the day before the exercise program began, all 50 men participated in a step-test. This (93) of stepping up and down on a 16-inch bench (94) 30 steps a minute for 5 minutes. One minute after completion of the step-test the pulse (95) of each subject was taken and recorded. This (96) as the pretest for the experiment. For the next 7 weeks, subjects in the experimental group (Group A) rode an Exercycle (a motor-driven bicycle-type exercise machine) for 15 minutes each day. The exercise schedule (97) for riders to ride relaxed during the first day's ride, (98) holding on to the handle bars and foot pedals (99) the machine moved. (100) , for the next 3 days, they rode relaxed for 50 seconds of each minute, and pushed, pulled, and pedaled actively for 10 seconds of each minute. The ratio of active riding was (101) every few days, (102) by the third week it was half of each minute, and by the seventh week the riders were (103) 15 solid minutes of active riding.
(104) end of the 7 weeks, the step-test was again (105) to both groups of subjects, and their pulses taken. The post-exercise pulse rates of subjects in the experimental group. (106) found to have decreased a(n) (107) of 30 heart beats per minute, with the lowest decrease 28 and th highest decrease 46. The pulse rates of subjects in the control group (108) the same or changed no more than 4 (109) , with a(n) (110) difference between the initial and final tests of zero.