Anything dropped falls towards the center of the earth because of ______.

单项选择题If a person finds getting up early a problem, most probably（）

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

单项选择题You are advised to rise with a yawn and stretch because it will （）

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