Question

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

Explanation:

To solve this, we recall lung anatomy: Bronchioles are small airways, not blood vessels or air sacs. Alveoli are tiny air sacs (not blood vessels) at the innermost part of lungs for gas exchange. So we eliminate options misidentifying bronchioles as blood vessels/air sacs or alveoli as blood vessels. The correct description is "tiny air sacs called alveoli".

Answer:

C. tiny air sacs called alveoli (assuming the third option is labeled C; if original labels differ, adjust to the option with "tiny air sacs called alveoli")