Which of the Following Situations Occurs in Electrically Excitable Cells

Multiple Choice

Which of the following situations occurs in electrically excitable cells?

A) When Na⁺ channels open, K⁺ channels close.
B) The sodium-potassium pump moves Na⁺ into the cell.
C) Depolarization causes voltage-gated Na⁺ channels to open.
D) Ligand-gated Na⁺ channels are opened by high extracellular Ca²⁺ levels.
E) Proteins tend to diffuse out of the cell.