When Colin Was Young He Was Stung by a Bee

Multiple Choice

When Colin was young he was stung by a bee and had a severe allergic reaction. Now, many years later, whenever he hears a buzzing sound (including when people imitate a buzzing sound) , he becomes nervous and panics. In this example, the conditional stimulus is

A) the bee.
B) the severe allergic reaction.
C) the buzzing sound.
D) Colin's reacting nervously and panicking.
E) the bee sting.