In the past, man did not have to think about the protection of his environment. There were few people on the earth, and natural resources seemed to be　36　. 
Today things are　 37　 , the world has become too　 38　 . We are using up our natural resources too quickly, and at the same time we are　39　 our environment with dangerous chemicals. If we continue to do this, human life on the earth will not 　 40　.
　　Everyone　41　 today that if too many fish are taken from the sea, there will soon be none left. Yet, with modern fishing　 42 , more and more fish are caught. We know that if too many trees are cut down, 　43　 will disappear and nothing will grow on the land. Yet, we　 44　 to use bigger and more powerful machines to　 45　 more and more trees.
We realize that if rivers are polluted with waste products from factories, we will die.　 46　 , in most countries wastes are　 47　put into rivers or into the sea, and there are　 48　 laws to stop this.
We know, too, that if the　 49　of the world continues to rise at the present rate, in a few years there will not be enough 50　.  What can we do to solve these problems ?
　  If  we eat more vegetables and less　 51　 , there will be more food available for everyone. Land that is used to grow crops　 52　 five times more people than land where animals are kept. Our natural resources will　 53　 longer if we learn to recycle them. The world population will not rise so quickly if people use modern methods of birth 54　 .
　　Finally, if we educate people to think about the problems, we shall have a better and clearer 55　in the future.

A．beautiful B．unlimited C．rare D．valuable

A．common B．the same C．changeable D．different

A．crowded B．small C．dirty D．busy

A．protecting B．saving C．polluting D．fighting

A．die B．survive C．keep D．satisfy

A．wonders B．realizes C．consider D．discovers

A．poles B．boats C．methods D．ideas

A．continue B．have C．ought D．go

A．grow B．plant C．save D．cut down

A．Thus B．However C．Otherwise D．Therefore

A．still B．even C．also D．certainly

A．too many B．a few C．some D．few

A．production B．pollution C．population D．revolution

A．houses B．vegetables C．food D．lives

A．fruit B．meat C．fish D．grain

A．feeds B．increases C．supplies D．helps

A．use B．stay C．keep D．last

A．control B．born C．plan D．reward

A．nature B．sea C．planet D．forest