Answer:
B. The rooster who attacked Calvin
Step-by-step explanation:
According to classical conditioning, the conditioned stimulus is the word rooster while the unconditioned stimulus is the rooster that attacked Calvin and the conditioned response is the twists in Calvin's stomach/feeling nervous.
Classical conditioning is a type learning whereby an unconditioned stimulus (the rooster who attacked Calvin) is associated with a conditioned stimulus (the word rooster) to elicit a conditioned response (twists in Calvin's stomach/feeling nervous) in a the subject.