Water is very important to us. We cannot live without it.There is a lot of water on the earth, but we cannot use most of it. About 97.4% of the earth’s water is salty. Most of the fresh(　　)water is snow and ice near the North and South Poles(　　).We can use only about one percent of the water on the earth. We use water from both lakes and rivers. Some of the water evaporates(　　)and then becomes rain. Of course we use rain water for farms and other things. We use this water again and again.Sometimes the earth’s water is in the wrong place. There is a lot of rain in the tropics(　　), but it is difficult to have farms in the tropics. Most of the land there is not very rich. Some desert land is rich, but there is only a little water in the desert.Water is a problem for many people in the world.单选题