Michael Is 12 Years Old and Is Undergoing Chemotherapy Treatment

Michael is 12 years old and is undergoing chemotherapy treatment. After his first chemotherapy treatment, Michael experienced nausea and vomiting. After several treatments, Michael now experiences anticipatory nausea as soon as he enters the treatment room and before he receives the chemotherapy. In this classical conditioning example, Michael's initial chemotherapy treatment would be considered the

A) conditioned response.
B) unconditioned response.
C) conditioned stimulus.
D) unconditioned stimulus.