Answer: The cat is the Unconditioned Stimulus
Explanation:An Unconditioned stimulus is me that sparks or triggers an unconditioned response;
For example, the cat is the unconditioned stimulus for the dog's reaction which in turn is an unconditioned response to the cat. We can also say that an Unconditioned Stimulus is any stimulus that causes or triggers an unlearnt/Unconditioned response.Another example of Unconditioned stimulus is Hunger, and we respond to it by eating.