单选题：hy does the speaker suggest we rise with a yawn and stretch?

hy does the speaker suggest we rise with a yawn and stretch? A．Because it will help keep your energy for the day's work.
B．Because it will help you to control your temper early in the day.
C．Because it will help you to' concentrate on your routine work.
D．Because it will keep your energy cycle under control all day.