Professor Kraig Is Known for His Difficult Quizzes,which Automatically Make

Multiple Choice

Professor Kraig is known for his difficult quizzes,which automatically make the students anxious.Immediately before each quiz,he always turns off the projector.Students soon notice
That they start to feel anxious when Professor Kraig turns off the projector.In terms of
Classical conditioning,Professor Kraig turning off the projector is a(n)

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