Answer:
Excercise can really boost our mood, increase our stamina, and strengthen our bones. Being fit can also decrease risk of desease.
I’m not exactly sure, but I’m thinking it may be A . I just learned about this unit previously .
They can enter your blood stream (via breathing/ingesting) and once in your bloodstream they can enter cells and mutate your dna, which can cause cancer/birth defects/ reproductive harm