MrSmart Tells His Students That They Can Do Whatever They

Mr.Smart tells his students that they can do whatever they want for the first ten minutes of class, but they must then turn their attention to the day's assignment.The students are delighted with their ten minutes of free time but do not subsequently attend to the assignment when it is time for them to do so.From an instrumental conditioning perspective, what mistake has Mr.Smart made?

A) The "reinforcer" is not contingent on the response.
B) Reinforcement is not immediate.
C) Free time is not an effective reinforcer for most students.
D) He has used negative reinforcement instead of positive reinforcement.