Which of the Following Does the Premack Principle State

Which of the following does the Premack principle state?

A) Primary reinforcers are the most effective rewards.
B) Things you are already doing for enjoyment can act as reinforcers for certain other behaviours you want to decrease in frequency.
C) An entire chain of responses must be completed before rewards are delivered.
D) Things you are already doing for enjoyment can act as reinforcers for certain other behaviours you want to increase in frequency.