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.