Answer: d. is especially active during the early phases of classical conditioning.
Explanation:Hippocampus is a special part of the limbic system of the brain,it is the part of the brain where conditioned response takes place,it also regulates emotional response,learning,memory etc.
THE HIPPOCAMPUS IS ESPECIALLY ACTIVE DURING THE EARLY PHASES OF CLASSICAL CONDITIONING.
Classical conditioning refers to a cognitive procedure in which a biologically potent stimulus is paired with a previously neutral stimulus.