Tetanic Muscle Contractions Don't Occur in a Normal Cardiac Muscle

Tetanic muscle contractions don't occur in a normal cardiac muscle because

A) the refractory period lasts until the muscle relaxes.
B) cardiac muscle tissue contracts on its own.
C) the refractory period ends before the muscle reaches peak tension.
D) neural stimulation is lacking.
E) potassium channels outnumber sodium channels.