No air means death. There is air around us  36 we can’t see it. Air is everywhere and it gives   37 　to every living thing. We can’t live  38  it. Bad air makes people ill. We must have fresh air to keep us  39 .
In the city there are a lot of people and there are too many  40  running on the road. The gas which the car sends out is made up of(组成) bad gases. Every day we  41  it in and        out. This makes us feel sick. There are many  42 , too. From the chimneys(烟囱) of these factories, we  43  get the smoke in black color. This kind of smoke is  44 to our health. So in order to keep us healthy, we have to go out to the   45  to breathe more fresh air. Or we can go up hills to get more fresh air.
A. because            B. though              C. so
A. life               B. name     　        C. pleasure
A. with               B. without         C. below
A. quiet              B. tall      　   C. healthy
A. dogs           B. trains     　  C. cars
A. breathe            B. draw      　   C. bring
A. animals            B. people          C. factories
A. usually  　　      B. never    　        C. seldom
A. helpful    　　    B. dangerous       C. necessary
A. office   　      B. city            C. Countryside