In an Experiment, the Pupils of Subjects' Eyes Contracted When

Multiple Choice

In an experiment, the pupils of subjects' eyes contracted when a bright light was shown. After continual pairing of the bright light with the sound of a bell, subjects' pupils contracted when they heard the bell. After pairing the sound of the bell with the experimenter's verbal instruction "Contract," pupil contraction occurred with just the verbal instruction. In this entire study, the conditioned stimulus is (stimuli are) the ________.

A) bell
B) bright light
C) word "contract"
D) bell and the word "contract"