No air, no life.  We can not see air, but there is air all a________ us and it gives life to every living things. We cannot live without it.  Bad air makes people i________.  We must have clean air to keep us in good health.

In the city there are a great many p______ and there are too many cars running on the road. That makes air dirty. Every day we take in dirty air. This makes us f______sick.

There are many cars and factories in the city.  The smoke is usually b_________. This is very bad for our health. So in order to get some fresh air, we should grow more trees.