Which statement is true? a. on a chain schedule, the longer the delay between a discriminative stimulus and primary reinforcement, the less effective it is as a conditioned reinforcer. b. on a chain schedule, the less the delay between a discriminative stimulus and primary reinforcement, the less effective it is as a conditioned reinforcer. c. on a multiple schedule, the longer the delay between a discriminative stimulus and primary reinforcement, the more effective it is as a conditioned reinforcer. d. on a multiple schedule, the longer the delay between a discriminative stimulus and primary reinforcement, the less effective it is as a conditioned reinforcer.