When Young Animals Are Raised in "Enriched" Environments, They Tend

When young animals are raised in "enriched" environments, they tend to have heavier brains with more dendrites and synapses and have higher concentrations of various neurotransmitters. Instances like these most clearly demonstrate how:

A) shaping can influence learning.
B) biology can influence learning.
C) classical conditioning can influence learning.
D) learning can influence biology.