This passage is mainly about________.

A．pressing his chin upwards is enough to get him breathing
B．blowing air into his mouth is sure to save his life
C．pressing his nostrils together with your fingers can work
D．pressing is the last chance of saving his life

A．If a man does not breathe for minutes, his brain will be completely destroyed.
B．If you see someone drowning, you must give him mouth-to-mouth breathing.
C．Don' t stop pressing his chest, if the drowning man starts breathing again.
D．When pressing, you can do it as hard as you can.