You are right. There are also chemicals from factories and plants.
What should we do to prevent this problem?
Hi Lan, I want to ask you some questions. Are you busy?
What is the cause of air pollution?
No, I am not. What do you want to ask?
Yes, and we should also use more public transport or walk to school.
I think we should plant more trees.
There are many causes. Smoke is one of them.