Classical conditioning is most successful when the neutral stimulus begins: long before the unconditioned stimulus begins. Immed
iately after the unconditioned stimulus begins. Just before the unconditioned stimulus begins. X at exactly the same time that the unconditioned stimulus begins.
I believe the answer is: just before the unconditioned stimulus begins.
By pairing the neutral stimulus with unconditioned stimulus on a short period of time, the subject would automatically perceive that both of them are strongly correlated. This speed up the creation of conditioned response that intended toward the subjects,.
