单项选择题
A．he is a lazy person B．he refuses to follow his own energy cycle C．he is not sure when his energy is low D．he is at his peak in the afternoon or evening
A．change his energy cycle B．overcome his laziness C．get up earlier than usual D．go to bed earlier
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 hours of day. C．Habit helps a person adapt to his own energy cycle. D．Children have energy cycles, too.