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 fewer than 10 trials.
C) the pig was difficult to train because it kept dropping the coin, rooting, and throwing the coin in the air.
D) the pig showed intrinsic interest in the task and so reinforcement was unnecessary.