单选题 In the past, man didn't have to think about the protection of his environment. There were few people on the earth, and natural resources seemed to be (56) . Today things are (57) . The world has become too (58) . We are using up our natural resources too quickly, and at the same time we are (59) our environment with dangerous chemicals. If we (60) to do this, human life on the earth will not survive.
Everyone (61) toady that if too many fish are taken from the sea, there will soon be none left. Yet, with modem fishing (62) more and more fish are caught. We know that if too many trees are cut down, (63) will disappear and nothing will grow on the land. Yet, we (64) to use bigger and more powerful machines to (65) more and more trees.
We realize that if rivers are polluted with waste products from factories, we will die. (66) , in most countries wastes are (67) put into rivers or into the sea, and there are (68) laws to stop this.
We know, too, that if the (69) of the world continues to rise at the present rate, in a few years, there will not be enough (70) What can we do to solve these problems?
If we eat more vegetables and less (71) , there will be more food available for anyone. Land that is used to grow crops (72) five times more people than land where animals are kept.
Our natural resources will (73) longer if we learn to recycle them. The world population will not rise so quickly if people use modem methods of birth (74) .
Finally, ff we educate people to think about the problems, we shall have a better and cleaner (75) in the future.