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Option b. is incorrect. Axons are long thin projections emanating from the cell body and conduct impulses away from the cell body. Option c. is incorrect. Dendrites are the projections on a neuron that receive impulses from other neurons. Option d. is incorrect. Neurotransmitters are chemicals that are secreted from the axon terminal when a neuron is stimulated. These substances initiate impulses in other cells. Option a. is correct. The neuron is the structural and functional unit of the nervous system.