（ ） are any of the small air spaces in the lungs where leaves the and oxygen enters it. A: Cilia B: Bronchioles C: Tracheae D: Pulmonary alveoli
（ ） are any of the small air spaces in the lungs where leaves the and oxygen enters it. A: Cilia B: Bronchioles C: Tracheae D: Pulmonary alveoli
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