Why does the size of population differ from place to place​

This is the answer of your question.

answer; i believe that the correct answer is (a) restriction);

the more fit you are, the faster the recovery. your heart rate drops most sharply in the first minute after you stop exercising; it should then fall about 20 beats a minute—a drop of less than 12 beats a minute is considered abnormal. this “recovery heart rate” is measured as part of an exercise stress test.