Samantha's Cat Salivates in Response to the Taste of Food

Multiple Choice

Samantha's cat salivates in response to the taste of food in its mouth.Each morning,Samantha places the cat's food on the back porch.When the door to the porch opens,a bell rings.So,each time Samantha opens the door the bell rings.Now,Samantha's cat salivates when the bell rings.Which of the following is the unconditioned stimulus in this example?

A) food
B) salivation
C) the door
D) the bell on the door