65.What’s the best title of the passage?

65.What’s the best title of the passage?
A.Stop polluting B.Change or leave
C.Look for a new home D.Return to the earth
答案A为什么不行?为何是答案D呢?
Ladies and gentlemen,I returned to this year in a time machine．In the year 2500,we are able to travel through time to any year in the history of the earth．This year is your last chance to change your lifestyle to save the earth.
Beginning in the middle of the 20th century,a few people were worried about polluting the earth’s water and air,but most people did not change their way of life．Instead,they continued to pour dangerous chemicals and other waste into lakes and seas,to drive more and more cars and trucks,and to cut down trees．
By the year 2200,the earth’s water was completely polluted．People could no longer drink water,and they had to use other types of liquids (液体)．Scientists said that in the future there might be too many people on the earth．But not enough was done．
So,by the year 2300,there were so many people that food became scarce．There was no water to grow food and all of the fish in the lakes and seas died because of pollution．Terrible wars (战争) broke out between the rich and the poor．Scientists were working very hard to find another planet in space where humans could live．
By the year 2400,the air was too polluted for humans to breathe (呼吸)．So we had to leave the earth．But only the rich were able to leave．Where did we go?Nowhere．You see scientists did not find another safe planet,so now we must travel around the universe in our spaceships．We are still looking for a place to call our home．
So,it is up to you to change history．There is still hope．You must change your lifestyle now,before it is too late．