Read the following passage and m...

Câu hỏi: Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 30 to 34.

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.