A group of scientists studied the effects of exercise on insulin sensitivity in elderly women. The scientists measured the amount of insulin secreted in the saliva when given glucose. Measurements were taken at 0, 20, 40, and 70 minutes after the glucose was administered. The graph shows the data collected before and after a four-month exercise program was put into place. Which statement BEST analyzes the data shown in the graph?
A. Elderly women secrete more insulin the more they exercise.
B. Exercise decreases insulin sensitivity in elderly women.
C. Insulin sensitivity is at its highest after 50 minutes.
D. Insulin sensitivity increases as exercise decreases.