完形补文：下面的短文有十处空白，每处空白后的括号内有一个词，请根据短文内容将其正确的形式填入文中，以恢复文章原貌。 In the past, man did not have to think about the (protect) of his environment. There were few people on the earth, and (nature) resources seemed to be (limited). Today things are different, and the world has become too (crowd). We are using up our natural resources too (quick), and at the same time we are polluting our environment with (danger) chemicals. If we continue to do this, human life on the earth will not survive. People realize today that if too many fish are (take) from the sea, there will soon be none left. Yet, with modern fishing methods, more and more fish are caught. We know that if too many trees are cut down, forests will (appear) and nothing will grow on the land. Yet, we use bigger and more powerful machines to cut down more and more trees. We realize that if rivers are (pollute) with waste products from (factory), fish will die. However, in most countries wastes are still put into rivers or into the sea, and there are few laws to stop this.