Answer: A
Explanation: The blood–air barrier (alveolar–capillary barrier or membrane) exists in the gas exchanging region of the lungs. It exists to prevent air bubbles from forming in the blood, and from blood entering the alveoli. ... The barrier is permeable to molecular oxygen, carbon dioxide, carbon monoxide and many other gases.
Answer:
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in the tiny air sacs (alveoli) at the end of the bronchial tubes.
Answer:
maintaining eye contact proves that you are paying attention to the person talking
