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We have only ______ Earth. We get land, air and water ______ the Earth. We should take care of them. We ______ keep them clean. Farmers grow food on land. Food from dirty land is ______ for us. We should keep land ______. We cannot build too ______ houses. There is not much land on Earth for farming. We should save land. Water is useful. We drink it and use it ______ many things. But there ______ much water in many places. In some places, dirty water from factories ______ the rivers dirty. People shouldn't ______ water.