Answer: a piece of candy at various times.
Explanation:
Variable interval (VI) schedule is the mechanism of operant conditioning for reinforcement scheduling.In this process response is imposed with reinforcement with particular amount passage of interval or gap.This mechanisms has variable schedule for time.
According to thew question, Lisa should implement the Variable interval (VI) schedule by providing participants with the candy at changing time in 10 hours of time period.Thus,it will help in better reinforcement of response in her experiment.