Why is the cell membrane so important to a cell A: the membrane is responsible for producing proteins
B: the membrane regulates the movement of molecules in and out of the cell
C: the membrane coordinates all of the cell’s activities

B

Explanation:

The plasma membrane, or the cell membrane, provides protection for a cell. It also provides a fixed environment inside the cell. ... And those proteins which stick outside of the plasma membrane will allow for one cell to interact with another cell. The cell membrane also provides some structural support for a cell.

they deliver oxygen to the blood

i think the answer would be d