"Environmental protection, people-oriented". Since June, 2000, the newly adjusted air quality index of Nanjing has pointed out a group of main factors affecting air quality in Nanjing.

First, harmful gases and dust. Harmful gases mainly include carbon monoxide, sulfur dioxide, nitrogen dioxide and other gases; Dust mainly refers to some small solid particles; Therefore, the option is correct;

B, oxygen is the main component of air and will not cause pollution; So the option is wrong;

C, nitrogen and oxygen are the main components of air, and will not cause pollution; So the option is wrong;

D nitrogen is the main component of air and will not cause pollution; So the option is wrong;

So choose one