Depolarization of a Cardiac Muscle Cell Occurs as the Result

Depolarization of a cardiac muscle cell occurs as the result of

A) a decrease in the permeability of the plasma membrane to Na⁺.
B) the opening of voltage-gated Na⁺ channels and voltage-gated Ca²⁺ channels.
C) the closure of voltage-gated Ca²⁺ channels.
D) the opening of voltage-gated K⁺ channels.
E) the closure of the voltage-gated Na⁺ channels.