Answer:
The answer is b) shaping.
Step-by-step explanation:
In this processs, the subject is exposed to a gradual change of stimuli in order to shape its behaviour. This is done through succesive approximations, which means the subject's behaviour is reinforced according to slightly different tasks.
For example, a rat is reinforced only after turning a lever. After it does the task regularly, the expected behaviour will be slightly different (e.g. reinforced only after standing at a certain distance from the lever).