Which role do ultrafine particles play in dirty air?

They contribute to less than 13,000 premature deaths a year.
They can worsen symptoms for people with breathing difficulties.
They are easily removed from the air when people see them floating.
They are constantly filtered by the nose, which prevents lung absorption.

They can worsen symptoms for people with breathing difficulties.

Explanation:

The other person is correct, I don't know what else to say because I don't want to feel like I'm copying them but I just wanted to confirm that their answer is in fact correct. :)

Explanation:

answer; ///(b) it is composed of four protein chains and four heme groups;

answer; i believe that the correct answer is (lung);