When Keller and Marian Breland, Two Psychologists Who Became Animal

When Keller and Marian Breland, two psychologists who became animal trainers, decided that it would be cute to have a pig drop a big wooden coin into a box, they found that __________

A) food was not an effective reinforcer for the pig and so learning didn't occur.
B) when given edible roots as reinforcers, the pig learned the task in less than ten trials.
C) the pig displayed instinctive drift by dropping the coin and pushing it around with its nose.
D) the pig showed intrinsic interest in the task and so reinforcement was unnecessary.