Which of These Is a Major Difference Between Smooth Muscle and Skeletal

Multiple Choice

Which of these is a major difference between smooth muscle and skeletal muscle?

A) Myosin is the main regulatory protein in smooth muscle.
B) Myosin is the main regulatory protein in skeletal muscle.
C) Skeletal muscle usually exhibits spontaneous activity,while smooth muscle cannot contract spontaneously. 
D) Only skeletal muscle requires increased calcium ion concentration in the cytosol for contraction.
E) Only skeletal muscle has both actin and myosin.