In the "lock and key" analogy of synaptic communication,which of the following is the "lock"

A)  the soma
B)  the receptor 
C)  the axon
D)  the neurotransmitter

Synaptic Communication

The process by which neurons communicate with each other through the release and reception of chemical neurotransmitters across the synaptic gap.

Receptor

A protein molecule that receives and responds to chemical signals from outside a cell.