1.  Firstly, the burning of petrol releases poisonous gases steadily, which has been one of the main factors of air pollution.

2.  As the industry develops faster, more waste gas are released into the sky and more waste water are poured into rivers.

3.  We go to work with our cars, thus releasing poisonous gases.

4.  There are some causes for the pollution, there are maybe the man cut the plants, discard the rubbishes, release the gases.

5.  They dump too much sewage into rivers and ocean, release poisonous gases into the air and bury solid wastes deep under ground.

6.  What's more, too many cars and buses are on the road, releasing gases as well, which plays a major role in the air pollution, too!