Answer: Reinforcement
Explanation: Bobby's habit is an operant response established through reinforcement.
An operant response is defined as a behavior that is changeable by its consequences with the probability of that behavior occurring again either increasing or decreasing.
Reinforcement as an operant response refers to anything that increases the likelihood that a response will occur. In this case, nagging from Bobby's mother. Reinforcement can range from a variety of events, rewards, situations etc that strengthens or increases a behavior when it is administered (positive reinforcement) or withdrawn (negative reinforcement).