The answer is letter C.
The operative word for the sentence is exercise. The effect of developing good endurance is caused by exercise. Exercises that are performed on a regular basis give individuals many beneficial effects to health and overall development. Individuals should at least exercise 30 minutes a day, 3-5 times a week in able to reap the benefits that it could bring to the body internally and externally. But before any training regimen, individuals should consult a physician to ensure that the activities to be performed will be safe.