When animal trainers Keller and Marion Breland tried to train a raccoon to drop a coin into a piggy bank, the animal would "wash" the coin instead. The difficulties the Brelands had in applying operant principles to animals demonstrate that
a. training with operant methods is largely ineffective.
b. there are biological constraints on learning.
c. the basic learning principles are different in humans and animals.
d. raccoons and humans did not have a common ancestor, proving that the theory of evolution is wrong.
Answer: B. There are biological constraints on learning.