The water and the land are thought part of the earth surface (表面). The air is 1 毯子) 2 洞穴) 4 in the earth. Did you think about the air that was in the cave? The land has some air mixed in it. Air is even mixed 5 the water in the sea. These examples show that some air is 6 the earth’s surface as well as above it. the earth. But it is 3 than that. Maybe you have been in a cave ( thought a kind of blanket (
