单项选择题
People and the sources of air pollution are found in the same places．This means that cities with large populations have the biggest problem of dirty air．Air pollution is caused by many different things．A major source of air pollution is the gas fumes from cars．Statistics show that 93 percent of all auto trips are within cities．Another major source of dirty air is the burning of coal and oil for energy．This energy is needed to make electricity．Of course，much more electricity is used in the city than in the country．
On the average，we throw away more trash and garbage than the year before．The burning of garbage contributes to air pollution．Many major industries are also responsible for the dirty air in the around cities．The fumes iron，steel，chemical，and petroleum production add particles to the air．
The effects of air pollution range from mild headaches to death．The levels of pollution found in heavy for traffic may cause headaches for loss of clear vision．Wherever coal and oil are used for fuel，fumes may kill trees and plants and cause metal to corrode．In some of the larger cities，these fumes endanger the life of human beings by contributing to lung diseases and causing early death．
Therefore, it's high time to stop making our living places unsuitable to live and killing ourselves.
A.they may cause mild headaches
B.they may cause problems with people's sight
C.they may cause lung diseases
D.they may lead to immediate deaths