The muscle relaxes if no new nerve signal arrives. however the neurotransmitter from the previous stimulation is still present in the synapse. the activity of to remove this neurotransmitter.
myosin
action potential
tropomyosin
acetylcholinesterase

acetylcholinesterase

Explanation:

Acetylcholinesterase is an enzyme responsible for disrupting neurotransmission in the nervous system through the neurosynaptic cleft or at the neuromuscular junction. This enzyme quickly and efficiently catalyzes the hydrolysis of acetylcholine in cholinergic synapses for acetate and choline.  Rapid destruction of acetylcholine deactivates the neurotransmitter after binding to the receptor to prevent its accumulation at synapses and to prevent the production of continuous stimuli by repetitive interactions.

the answer to your question is b