There are a lot of trees around us. The trees can help to make the air 【小题1】 and cleaner. They can also help to 【小题2】 the weather. They provide(提供) humans with food，【小题3】, medicine and other things. Because of the trees, many animals can live 【小题4】 the earth. But people often cut trees down in large numbers. The forests are becoming much 【小题5】 than before, so we should protect them well.