複選題28. There is an electric potential across the plasma membrane of a living animal cell. Which of the following statement(s) about membrane potential is/are correct? (A) There are many open K+ channels but not so many open Na+, Cl- or Ca2+ channels on the surface of a living animal cell. (B) Moving K+ outward by K+ channel causes an excess of positive charge outside the cell (C) The drive force for moving K+ ion outward is the K+ concentration gradient across plasma membrane. There is an excess of K+ ion inside the cell (D) Na+/K+ ATPase is needed to maintain an excess of K+ ion inside the cell (E) Therefore, ATP is required to maintain membrane potential in a living animal cell.