The correct option is D Acetylcholine
Neurotransmitters are the chemicals, which allow the transmission of signals from one neuron to the next across synapses. They are also found at the axon endings of motor neurons, where they stimulate the muscle fibres. Acetylcholine was the first neurotransmitter to be discovered. It is synthesized by enzyme choline acetyltransferase. After releasing it binds with its receptor present at the postsynaptic terminal. Then it is soon hydrolyzed by an enzyme acetylcholinesterase.