The answer is letter C.
Aerobic activities help the heart to pump blood at an increase rate with each heartbeat. The heart is a muscle, therefore through exercise, these muscles are also developed the same way that the skeletal muscles are. When the heart becomes strong it tends to pump less but with a more forceful action causing blood to instantaneously flow all over the body systems. Aerobic activities that last for 30 minutes are enough to cause the heart to pump extra and get developed into a strong muscle.
