Question

the innermost parts of the lungs are the... tiny air sacs called bronchioles. tiny blood vessels called alveoli. tiny air sacs called alveoli. tiny blood vessels called bronchioles.

Explanation:

Alveoli are tiny air - sacs in the lungs where gas exchange occurs. Bronchioles are airways, not blood vessels. Alveoli are the innermost parts for gas exchange.

Answer:

C. tiny air sacs called alveoli.