A layer (层) of air surrounds our earth completely. We call it the atmosphere (大气层，气氛). Without the atmosphere, we shall not be able to live on the earth. There will be no air for us to breathe. The earth will be very, very hot in the day and very, very cold during the night.

　　Air is all round us. It is around us as we walk. When we sit down, it is around us. When we go to bed, air is also around us. We live in air.

　　All living things need air. Living things cannot live without air. We can go without food or water for a few days, but we cannot live for a few minutes without air. We breathe in air.

　　We need air in order to live. Do you know that fires too need air in order to burn? If there is no air, you will not be able to make a fire.

　　We know that air is around us everywhere. We cannot see air but we can feel it. Simple experiments will show that air occupies space and has weight.

 69.Which of the following is not mentioned in the passage?

　　We live in air.　

　　Air is atmosphere.　

　　We breathe in air.　

　　Air is a mixture (混合物，混杂).　

 70.The passage tells us that air is 　　 atmosphere.

　　just the same as　

　　quite different from　

　　very much like　

　　something like　

 71.The best title (标题) for this passage would be 　　.

　　Air　

　　Air Surrounds Our Earth　

　　All living Things Need Air