If you see someone drowning, speed is very important. Once you get him out of the water, i

f he isn't breathing, you have four minutes before his brain is completely destroyed. Support his neck, lift his head back and press his chin (下巴)upwards. This stops the tongue blocking the airway in the throat and is sometimes enough to get him breathing again. If that doesn' t work, start mouth-to-mouth breathing. Press his nostrils (鼻孔)together with your fingers. Open your mouth and take a deep breath. Blow into his lungs until his chest rises, then remove your mouth, and watch his chest fall. Repeat twelve times a minute. Keep doing until help arrives.

To bring a child back to life, keep your lips around his mouth and gently blow into his mouth. Give the first four breaths as possible to fill the blood with oxygen. If, in spite of your efforts, he starts turning a blue-grey color, you can feel no pulse (脉搏), then pressing is the last chance of saving his life.

With arms straight, rock forwards, pressing down on the lower half of the breastbone(胸骨). Don't be too hard or you may break a rib(肋骨). Check how effective you are doing if his color improves or his pulse becomes independent to your chest pressing. If this happens, stop the pressing. Otherwise continue until rescue arrives.

This passage is mainly about________.

A．how to save people out of the water

B．how to give first aid to people who are drowning

C．how to mouth-to-mouth breathing

D．how to save a child from a river