"Instinctual Drift" Is the Answer to Which Question

"Instinctual drift" is the answer to which question?

A) What animal behavior demonstrates that any response that is instinctually predisposed can be learned through classical conditioning?
B) What animal behavior demonstrates that any response that is instinctually predisposed can be learned through operant conditioning?
C) What is the tendency for animals to gradually return to an innate, instinctual response after learning a less natural response?
D) What is the tendency for animal behavior to instinctively drift closer and closer to biologically predisposed responses during the acquisition of new responses learned through operant conditioning?