Read the following passage and mark the letter A, B, C, or D on your answer answer to each of the questions

A. The economic impact of air pollution

B. What constitutes an air pollutant

C. How much harm air pollutants can cause

D. The effects of compounds added to the atmosphere

A. negatively

B. quickly

C. admittedly

D. considerably

A. water vapor is an air pollutant in localized areas

B. most air pollutants today can be seen or smelled

C. the definition of air pollution will continue to change

D. a substance becomes an air pollutant only in cities

A. They function as part of a purification process.

B. They occur in greater quantities than other pollutants.

C. They are less harmful to living beings than are other pollutants.

D. They have existed since the Earth developed.