Answer: d. shaping
Step-by-step explanation:
This is a method used to establish a particular behavior that someone hasn't learnt by introducing if slow by slow until it reaches a desired behavior.
This involves successive steps of reinforcing a behavior until it is completely grasped.
The steps that are used in reinforcing this behaviour are closely associated with the behaviour that need to be reached at the end.
For example a baby is given a candy so that he can utter the word for candy which is a first step towards shaping him to learn to communicate
A reinforcement need to be kept up until the person has learned the behavior.