The correct answer is option (D) store and release neurotransmitters.
The function of synaptic vesicles inside the axon terminals is to store and release the neurotransmitters. A synapse refers to the junction between the two neurons which transmit the nerve impulses by the diffusion of a neurotransmitter. Synaptic vesicles ar important for the transmission or the conduction of the nerve impulses as they store and release the neurotransmitters.
These neurotransmitters are the chemicals that transmit an impulse between two neurons or a neuromuscular junction. A neurotransmitter is released by the synaptic vesicle of one neuron into a region between the two neurons called the synapatic cleft. From here, it reaches the neurtransmitter receptors present on the target neuron, thus conducting the impulse. Examples of neurotransmitters include the epinephrine, histamine, acetylcholine and others.