Answer:
Biological predisposition.
Step-by-step explanation:
Operant conditioning may be defined as the form of the learning that are mainly associated with the punishments and rewards of an individual. John B. Watson introduces the concept of operant conditioning.
The learning of the pigs to pick the coins and its deposition in the bank is considered as rewarded with some conditions. The biological predisposition occurs in the memory of the pigs as this increases the likelihood works of the pigs.
Thus, the correct answer is option (d).