I think the answer is either B. or D.
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The respiratory system brings air into the lungs supplying the blood with oxygen. Oxygen is carried throughout the body to the organs and keeps the heart pumping and when the blood circulates back to the lungs the process starts over again.
Answer:
The cell structure is the plasma membrane also known as the cell membrane.
Explanation:
The plasma membrane is the thin coat of lipids (phospholipids) that surrounds and encloses a cell, also can be called the cell membrane
