Synaptic plasticity (i.e., changes in the structure or biochemistry of synapses that alters postsynaptic receptors) has been demonstrated most frequently in which psychological phenomena?

Synaptic plasticity (i.e., changes in the structure or biochemistry of synapses that alters postsynaptic receptors) has been demonstrated most frequently in which psychological phenomena:

A ) motivation
B ) stress
C ) learning
D ) emotions
E ) perception