填空题

Do you know what lungs (肺) are like (11) are in the upper part of our bodies. We have two of them. There are thousands of little pipes (管子) going through them. The (12) are like the branches of a tree and they go through every part of each lung. When we breathe in, air goes through the nose and mouth and travels down a large pipe. The other end of this pipe becomes two smaller pipes and each goes into one lung. (13) passes through those pipes and is carried around the body.
When you (14) , your upper body moves in and out. To breathe in, air rushes into your lungs. To breathe out, air is forced out of your lungs. The air we breathe goes into every part of the lungs through the branching pipes. They take it to the (15) which is moving all the time through the lungs and round to every part of our bodies. The blood goes around our body and back to the lungs in a very short time.