The plasma membrane or the cell membrane is the one that protects the cytoplasm of a cell. It is mostly composed of lipids and proteins. It has a phospholipid bilayer that controls the entering and exiting of molecules in the cell and at the same time, provides protection for the cell or plasma membrane. Proteins embedded within the phospholipid bilayer have the same function of the plasma membrane that includes selective transport. The phospholipid bilayer consists mainly of the lipid molecules. The answer is letter B.