Mrs. Ridcully, a dog trainer, is struggling to train a dog to learn a new trick. Mrs. Ridcully classically conditioned the dog to sit whenever she whistled. However, the dog responds only to Mrs. Ridcully’s specific whistle, not to the whistle of the dog’s owner (who hired Mrs. Ridcully to train the dog). Which learning principle is causing this difficulty?

stimulus discrimination

Explanation:

Mrs. Ridcully probably attempted that her conditioning (her own specific whistle) would eventually be generalized and other similar stimulus (dog owner's whistle) would generate the same conditioned response, but she failed. Instead, the dog discriminates Mrs. Ridcully's whistle from other people's whistle and will only respond to her.

Stimulus discrimination happens when the subject is able to differentiate between different stimuli, and will only respond to an specific stimulus.  

i do not get the question.

answerfull dress rehearsal;