What causes the cold air at the top of a mountain to sink at night?

Why do you think that air pollution is often worse in cities than in rural areas?

I don't know the first one but I think I know II

Explanation:

there there are more people people in cities than there are in rural areas and because of this more people will breathe cough get sick and pull it the air. plusplus there are no plants to keep the air clean but there are plants in rural areas.

learn it on the intertant so you can solve

i need the answer to this too but idk it ; -;