The correct answer is generalization.
Generalization refers to a concept in classical conditioning wherein stimuli similar to the conditioned stimulus also elicit a similar response. In this case, the conditioned stimulus (CS) is the sound of the electric can opener, and the response is the cat coming to the kitchen. Due to generalization, the new stimulus (sound of the electric drill) leads to the response in the cat, since this stimulus is similar to the CS (sound of the electric can opener).