In the past, man did not have to think about protection of the environment. There were very few people on the earth, and natural resources seemed to be unlimited. Today things are different. The world has become too crowded. We are using up our natural resources too quickly, and at the same time we are polluting our environment with dangerous chemicals. If we continue to do this, human life on the earth will not survive. Everyone realizes today that if too many fish are taken 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 disappear and nothing will grow on land. Yet, we continue to use more powerful machines to cut down more and more trees. We realize that if rivers are polluted with waste products from factories, we will die. However, in most countries waste is still put into rivers, but there are few laws to stop this. We also know that if the population of the countries in the world is to rise at the present rate in a few years, there will not be enough food. What can we do to solve these problems? If we eat more vegetables and less meat, there will be more food available for everyone. Land that is used to grow crops can feed five times more people than land where animals are kept. Our natural resources will last longer if we learn to recycle them. The world population will not rise so quickly if people use modern methods of birth control. Finally, if all of us think about the problem, we will have a better and cleaner planet in the future. From the passage we can see that the world's natural resources   _  .
will never be used up are being polluted are as plentiful as in the past are being used up very quickly