What Is the Role of Calcium in Muscle Contractions

What is the role of calcium in muscle contractions?

A) to break the cross-bridges as a cofactor in the hydrolysis of ATP
B) to bind with troponin,changing its shape so that binding sites on the actin filament are exposed
C) to transmit the action potential across the neuromuscular junction
D) to spread the action potential through the T-tubules
E) to re-establish the polarization of the plasma's membrane following an action potential