Ca²⁺-Pumps in the Plasma Membrane and Endoplasmic Reticulum Are Important

Ca²⁺-pumps in the plasma membrane and endoplasmic reticulum are important for

A) maintaining osmotic balance.
B) preventing Ca²⁺ from altering the activity of molecules in the cytosol.
C) providing enzymes in the endoplasmic reticulum with Ca²⁺ ions that are necessary for their catalytic activity.
D) maintaining a negative membrane potential.