Answer: 2. It is based on the idea that the number of times a behavior must occur before it is rewarded changes over time.
Step-by-step explanation:
A variable-ratio schedule is a schedule of reinforcement where a response is reinforced after an unpredictable number of responses. This schedule creates a steady, high rate of responding. It is believed that the more you carryout a certain behavior, you are likely to have a positive outcome.