4.  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, the pulse rate of each subject was taken had recorded. This served 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 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 ratio of active riding was increased every few days, so that by the third week it was half 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 were 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 28 and the highest decrease 46. The pulse rates of subjects in the control group remained the same or changed no more than 4 beats, with an average difference between the initial and final tests of zero.(5分)
4.1How many people were in each group?____(1分)
A. 100.
B. 50.
C. 25.
D. 15.