'Variable interval' schedule is demonstrated as the schedule in which a particular response or action is after an uncertain period of time which could be few hours, day, a week, etc. in order to reinforce a particular behavior or response.
In the given example, I('you' in the example) is studying as the pop quiz can be taken any time throughout the class which exemplify the 'variable interval'. <u>The 'variable interval' has been employed for free-operant conditioning to reinforce a specific behavioral response(studying) through inconsistent rewarding schedule.</u> Therefore, <u>'variable interval'</u> is the answer.
