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.

　　Many countries don't let people burn（燃烧）____7____ for air in houses and factories in the city. Pollution by 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 not 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 ff they ride to work. It's because the number of cars on the roads becomes larger. So more people ____9____ their bikes and go to work by ear, 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 ears into the city that they will go back to using their bikes.

　　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 roads 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 drive their cars into the city that they will go back to use their bikes.

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