Answer:
A. slowly and safely raises heart rate.
Explanation:
Many people believe that a warm-up period before working out is no needed, but this is absolutely wrong. Warming up the muscles will "adjust" them to exercise, also it will increase your heart rate.
Muscles need oxygen to their function, and they get it trough oxygenated blood. So, raising the heart rate will improve muscles functions, giving them the need oxygen. The result of this is a longer endurance during workout, even prevent muscle cramps.
