12. The two monolayers of the plasma membtane in a human red blood celt :
(A) both contain gangliosides.
(B) both contain glycolipids.
(C) have the same abundance of phosphatidylinositol.
(D) exchange phospholipids only through spontaneous flip-flops.
(E) have different overall elcctrical charges, with negatively charged phospholipids
(c.g. phosphatidylserine) normally enriched in the inner monolayer.