完形填空

　　The earth is our home．We must take care of it．Life today is easier than it was 　　1　　 years ago, but it has brought some new problems．One of the biggest problems is pollution(污染)．We can see it, smell it, drink it and even hear it．

　　Man has polluted the 　　2　　．The more people, the more pollution．Many years ago, the problem was not so serious because there were not so 　　3　　 people．When the land was used up(用光)or the river was not clean in a place, man went to 　　4　　 place．Now man is slowly polluting the whole world．

　　　　5　　 pollution is still the most serious．It's bad for 　　6　　 things in the world．

　　Many countries don't let people burn(燃烧)　　7　　 for air in houses and factories in the city．Pollution by SO₂ is now the most dangerous kind of air pollution．It's caused by(由……引起)heavy traffic．People say it's 　　8　　 to ride bikes．When you are riding, there is no pollution．But even in developed countries, most people don't go to work by bike．

　　It's not because bikes are expensive or people are tired if they ride to work．It's because the number of cars on the road becomes larger．So more people 　　9　　 their bikes and go to work by car, then things are getting worse and worse．We should have special(特别的)roads only for bikes and make it 　　10　　 difficult and expensive for drivers to take their cars into the city that they will go back to using their bikes．

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