Final answer:
Acetylcholine is the neurotransmitter among the given options, responsible for transmitting signals in the nervous system.
Step-by-step explanation:
The substance that acts as a neurotransmitter among the given options is acetylcholine. Acetylcholine is a chemical messenger that transmits signals across synapses in the nervous system. It is involved in various functions, including muscle movement, memory, and learning. An example of acetylcholine's role is its effect on muscle contraction in the neuromuscular junction.
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