Câu hỏi:

Read the following passage and choose the correct answer to each of the questions below.

Since the early 1980s, we began to worry about the bad effects of environmental pollution. It is the result of industrialization and of the careless use of the natural resources. Avoiding pollution is not easy. Many people try not to inhale traffic fumes and keep away from chemical waste by wearing mask when they get out of their house. Actually, indoor pollution is becoming more and more serious. They have found that dishwasher, washing machines, air conditioners, freezers, and refrigerators emit some certain toxic chemicals into the air. We surely inhale these chemicals when doing housework. Using gas cookers and burning candles produce carbon monoxide.

Therefore, before worrying about environmental pollution when going out, we should consider the problems of indoor pollution.

Pollution _______.