If one wants to work more efficiently at his low point in the morning, he should ______.

A．Getting off to work with a minimum effort helps save one's energy.
B．Dr. Kleitman explains why people reach their peaks at different hour of day.
C．Habit helps one adapt to his own energy cycle.
D．Children have energy cycles, too.

A．help to keep your energy for the day's work
B．help you to control your temper early in the day
C．enable you to concentrate on your routine work
D．keep your energy cycle under control all day