Contraction of a Skeletal Muscle Cell Is Initiated by the

Contraction of a skeletal muscle cell is initiated by the

A) release of acetylcholine by a neuron terminating at the neuromuscular junction.
B) release of calcium ions by the neuron into the neuromuscular junction.
C) electrical current traveling from the neuron directly into the muscle cell.
D) hormones delivered by the blood supply to the nearby tissue.
E) release of sodium ions by the neuron into the neuromuscular junction.