The hardest behavior modification technique to implement and understand is

A. desensitization.

B. habituation.

C. counter-conditioning.

D. punishment.

The hardest behavior modification technique to implement and understand is counter-conditioning technique. The correct option among all the options given in the question is option "C". Counter-conditioning technique is the technique of training where an animal is made to perform a task against its natural behavioral pattern. This can be very hard to implement.