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, the subjects' pupils contracted when they heard the bell. After the pairing of the sound of the bell with the presentation of a black square, pupil contraction occurred with just the sight of the square. In this entire conditioning study, the conditioned stimulus is (stimuli are) the ________.

A) bell and square
B) light and square
C) square
D) bell