Answer: Primary reinforcer
Step-by-step explanation:
Primary reinforcer is the reinforcer that is used for fulfilling biological requirements or needs in the form of rewards. These reinforcers do not require pre-learning or potential .Example of primary reinforcer -food, water, shelter etc.
According to the question, treat is considered as primary reinforcer which is achieved by Fluffy because it satisfied his biological needs when he performed sitting activity as per Chris's command.