Which of the following are roles played by calcium ions in coordinating the activation of a muscle by motor neurons?

A)Calcium ions enter the motor endplate of the muscle fiber, causing depolarization of the muscle cell.
B)Calcium ions enter the motor neuron axon terminus to stimulate vesicle fusion and neurotransmitter release into the neuromuscular synapse.
C)Calcium ions are released from the sarcoplasmic reticulum and bind with troponin to open actin binding sites for myosin, leading to force generation.
D)Calcium ions diffuse into the sarcoplasmic reticulum to open actin binding sites for myosin, leading to force generation.
E)Calcium ions are actively pumped into the sarcoplasmic reticulum to cause muscle relaxation by allowing tropomyosin to block actin binding sites.