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We have only one _____. We get land (土地), air and water from the Earth. We should _____ these things. We should keep _____ clean.

Farmers grow _____ on land. Food from _____ land is bad for us. We should keep the land clean. We cannot build too many houses. There is not much land _____ Earth for farming. We should save land.

We all need water. We cannot live _____ water. We drink it and use it _____ many things. But there is not much water in many places. In some places, dirty water from factories pollutes (污染) the rivers. Some people waste water.

We should take care of the _____ too. We need it to _____.