Let's Say You Have a Hungry Cat in Your Kitchen

Let's say you have a hungry cat in your kitchen.You use your electric can opener,which makes a rather loud sound,to open a can of cat food.You have done this many times before.The hungry cat comes running toward the kitchen at the sound of the can opener,not at the sight of the food.In this example,the sound of the can opener is the

A) conditioned stimulus.
B) conditioned response.
C) unconditioned stimulus.
D) unconditioned response.