Answer:
b. conditioned stimulus
Step-by-step explanation:
Conditioned stimulus is a previously neutral stimulus that, when associated with the unconditioned stimulus cause a trigger of a conditioned response. The conditioned stimulus acts a trigger to a conditioned response anytime it is paired or associated with a unconditioned stimulus. An example is a hotel concierge begins to respond every time he hears the ringing of a bell, this is because the bell has become associated with customers needing assistance, the bell has become a conditioned stimulus.