When the Brelands Tried to Teach Pigs and Raccoons to Drop

When the Brelands tried to teach pigs and raccoons to drop a coin in a box, the animals:

A) learned the trick only if explicit reinforcement was provided for doing so.
B) learned the trick if food was used as a reinforcer, but did not learn the trick if secondary reinforcement was used.
C) had difficulty learning the trick because it competed with their biological tendencies.
D) failed to learn the trick, indicating the some animals evolved to be resistant to operant conditioning.