Read the passage and fill in the blanks with proper words. （在短文的空格内填入适当的词，使其内容通顺，每空格限填一词，首字母已给）

    The earth is our home. We must take cof it. That is to say we must keep the land, a and water clean. But people began to pollute the earth after he first made a fire, washed his cin the river and threw dirty things on the ground. Many years ago, pollution was not so serious(严重的)bthere were not so many people.

    There was enough clean water and land. When the land or the river was din one place, man moved to another place. But now man is slowly polluting the whole world and there is not enough clean land or water. More people, more pollution.

    How shall we end all this？Is it pto get rid of (摆脱)pollution？We are glad to say that people have come to know the d  of pollution and a lot of people are working hard to get rid of it.