Toby's dog, Izzie, gets very excited when she sees her leash because she knows they are going for a walk. Today, Toby replaces Izzie's leash with a new one and brings it over to her to get ready to go outside. Toby is surprised because Izzie doesn't seem as excited as usual. This is MOST likely because Izzie has:a) spontaneously recovered the previously conditioned response from the old leash. b) discriminated between the two leashes, noticing that they are different. c) generalized from one leash to another. d) learned to respond to all leashes in the same way.