classical conditioning occurs when the question 70 options: a) unconditioned stimulus (us) is followed by, or associated with, a conditioned response (cr). b) neutral stimulus (ns) is followed by, or associated with, an unconditioned stimulus (us). c) unconditioned response (ur) occurs at the same time as the conditioned response (cr). d) unconditioned stimulus (us) is preceded by the conditioned response (cr).