Complete the following passage.
People need to breathe. If they don't breathe, they will die. But how clean is the air people breathe? If they breathe (1) __________ air, they will have breathing problems and become ill. Plants and animals need clean air too. A lot of things (2) __________ our lives create harmful gasses and make the air dirty, like cars, motorbikes and factories. Dirty air is called " (3) __________ air". Air pollution can also make our Earth (4) __________. The problem of air pollution started with the burning of coal in homes and factories.
Question 2:
A. at
B. in
C. to
D. on
