The correct option is B Synaptic vesicles
A neuron has 3 parts - cell body, axon and dendrites. At a chemical synapse, the membranes of the presynaptic neurons and postsynaptic neurons are separated by a fluid-filled space called synaptic cleft.
The prefixes "pre-" and "post-" reflect the direction of synaptic transmission: presynaptic is the transmitting side (synaptic knob) and postsynaptic is the receiving side (dendrite, soma, or effector). Synaptic knobs contain many membrane-bounded synaptic vesicles.