Life today is easier that it was hundreds of years ago,but it has brought some new problems,One of the biggest problems is pollution(污染).(A)We can see it ,drink it and even hear it.
Man has polluted the earth.(B)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 or the river was not clean in a place,man went to another place.Now man is slowly polluting the whole world.
Air pollution is still the most serious,it’s bad for living things in the world.
Many countries don’t let people burn(C)“有害物质”for air in houses and factories in the city.Pollution by SO2 is now the most dangerous kind of air pollution.It’s best 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 put away their bikes and go to work by car,then things are getting worse and worse.We should have special roads only for bikes and make it so difficult and expensive for drivers(D) (take)their cars into the city that they will go back to using their bikes.