Which letter correctly labels the synapse?

According to a source, the answer is A.

Synaptic cleft or the terminal buttons that transmits neurotransmitters to the next neuron, received by its dendrites and is relayed now throughout the system until it reaches the brain.

The messages must travel the distance of the nerves to the brain which are processed and made decisions, from the distance of the nerves from the sense organs, then travel back to the muscles that need to respond through the nerves.