The answer is letter D.
Exercise
is the operative word in the sentence which is the cause of gaining aerobic
endurance. The other words are not an indication of the cause of aerobic
endurance. Exercising plays an important role in overall fitness. It is always
beneficial and has no known negative side effects. All persons should aim to
exercise at least thirty minutes a day, three times a week. This improves
overall health and is linked to preventing
chronic diseases from happening to the body.
