10．The earth is our home．We must take care of it．Life today is easier than it was hundreds of years ago，（33）B 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 （34）A it．
Man has polluted the earth．The more people，the more pollution．Many years ago，the problem was not so serious because there were not so many （35）C．When the land was used up（用光） or the （36）D was not clean in a place，man went to other place．Now man is slowly polluting the world．
Air pollution is still the most serious，it's bad for living things in the world．
Many countries don't let people burn something （37）D 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 heavy traffic．People say it's best to ride bikes．Because when you are riding，there is no pollution．But even in developed（发达的） countries，most people don't go to work by （38）C．It's because the number of cars on the roads becomes larger．So more people put away their bikes and go to work by car，then things are getting worse and worse．We should have special（特别的） （39）B only for bikes and make it so difficult and expensive for drivers to take their cars into the city that they will go back to （40）A their bikes．
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Man has polluted the earth．The more people，the more pollution．Many years ago，the problem was not so serious because there were not so many （35）C．When the land was used up（用光） or the （36）D was not clean in a place，man went to other place．Now man is slowly polluting the world．
Air pollution is still the most serious，it's bad for living things in the world．
Many countries don't let people burn something （37）D 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 heavy traffic．People say it's best to ride bikes．Because when you are riding，there is no pollution．But even in developed（发达的） countries，most people don't go to work by （38）C．It's because the number of cars on the roads becomes larger．So more people put away their bikes and go to work by car，then things are getting worse and worse．We should have special（特别的） （39）B only for bikes and make it so difficult and expensive for drivers to take their cars into the city that they will go back to （40）A their bikes．
| 33．A．if | B．but | C．and | D．or |
| 34．A．hear | B．know | C．catch | D．use |
| 35．A．animals | B．trees | C．people | D．hills |
| 36．A．trees | B．land | C．grass | D．river |
| 37．A．new | B．old | C．good | D．bad |
| 38．A．train | B．car | C．bike | D．air |
| 39．A．money | B．roads | C．city | D．people |
| 40．A．use | B．buy | C．borrow | D．mend． |