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  3. Fifty volunteers were alphabetically divided into two equal groups. Group A to participate in a 7-week exercise program, and Gro

Fifty volunteers were alphabetically divided into two equal groups. Group A to participate in a 7-week exercise program, and Gro

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问题      Fifty volunteers were alphabetically divided into two equal groups. Group A to participate in a 7-week exercise program, and Group B to avoid deliberate 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 consisted of stepping up and down on a 16-inch bench at 30 steps a minute for 5 minutes. One minute after completion of the step-test, a pulse rate of each subject was taken and recorded. This served as the pretest for the experiment. For the next 7 weeks, subjects in the experimental group (Group A) rode an exercycle for 15 minutes each day. The exercise schedule called for riders to ride relaxed during the first day’s ride, merely holding on to the handle bars and foot pedals as the machine moved. Then, 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 ration of active riding was increased every few days, so that by the third week it was haft of each minute, and by the seventh week the riders were performing 15 solid minutes of active riding.
     At the end of the 7 weeks, the step-test was again given to both groups of subjects, and their pulses taken. The post exercise pulse rates of subjects in the experimental group were found to have decreased an average of 30 heart beats per minute, with the lowest decrease of 28 and the highest decrease of 46. The pulse rates of subjects in the control group (Group B) remained the same or changed no more than 4 beats, with an average difference between the initial and final tests of zero.
The step-test was given ______.
选项 A、at the beginning and at the end of the 7-week period
B、after each exercise period
C、only at the beginning of the 7-week period
D、only at the end of the 7-week period
答案A
解析 由文中可知，在为期7周的实验始末分别进行了一次阶梯测试。
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