Answer:
C) A variable interval reinforcement schedule
Step-by-step explanation:
A variable interval reinforcement schedule is the opposite of a fixed interval reinforcement schedule. If a variable interval schedule is used, the time that passes between response and the reward used as reinforcement is not fixed, it is generally unpredictable and changing.
In this case, the time intervals for handing out bonuses are set at 70 days and 100 days, but they usually happen around day 85, a few days more or less.