C. Synaptic vesicles release acetylcholine molecules.
Explanation:
A neuromuscular junction is the junction between the terminal part of a motor axon and a motor plate (or neuromuscular synapse), which is the region of the plasma membrane of a muscle fiber (the sarcolemma) where the nerve and muscle meet allowing to trigger muscle contraction.
At the neuromuscular junction, the neurotransmitter used is acetylcholine, which is released by the synaptic vesicles at the beginning of the signal transmission process through the neuromuscular junction. The nerve fiber branches off at the end to form the end plate. which invaginates into the muscle fiber, but rests entirely on the outside of the membrane.
