The earth is (we) home. We must take care of it. Life today is easier than it was hundreds of years ago, but it (bring) some new problems. One of the biggest problems (be) pollution. We can see it, smell it, drink it and even hear 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 people. When the land was used up(用光) or the river was not clean in a place, man went to another place. Now man is (slow) polluting the whole world.
Air pollution is still the most serious. It's bad for (live) things in the world.
Many (country) don't let people burn(燃烧) anything bad 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 best (ride) bikes. When you are riding, there is no pollution. But even in developed countries, most people don't go to work (介词) 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 put away their bikes and go to work by car, then things are getting worse (连词) worse. We should have special roads 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 use their bikes.
