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

A．resources B．sources C．materials D．matter

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

A．crowded B．polluted C．dirty D．busy

A．producing B．using up C．reducing D．making

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

A．try B．continue C．stop D．have

A．live B．last C．continue D．survive

A．fish B．seagulls C．crocodiles D．frogs

A．poles B．boats C．methods D．ideas

A．mountains B．the sea C．crops D．forests

A．grow B．plant C．save D．cut down

A．plant B．cut down C．save D．burn down

A．Thus B．However C．Generally speaking D．Therefore

A．encourage B．neglect C．stop D．wake up

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

A．pollution B．environment C．questions D．problems

A．fruit B．meat C．fish D．grain

A．use B．stay C．keep D．last

A．raise B．rise C．run D．grow

A．force B．help C．educate D．show