For extinction to occur, which of the following must be true of the conditioned response (CR), the conditioned stimulus (CS), and the unconditioned stimulus (UCS) ?

The CR occurs after the CS but does not occur after other stimuli.

The CS is repeatedly presented in the absence of the UCS, and the CR loses strength.

The CR occurs after a stimulus that is similar to the CS.

When the CR loses strength, a rest period is given, after which the CS again elicits the CR.