After curriculum and environmental modifications, as well as a strong history of reinforcement, Nawat is not only signing "break" when he needs one, but he also is working for longer periods of time. The team decides that Nawat's request for a break will be honored the first time he asks after he works an average of 5 minutes (the average on-task time last week was 4-7 minutes, so the criterion is reasonable). This means his request will be honored after he works for 3 minutes, 6 minutes, 2 minutes, 4 minutes, and so on. This is a [ Select ] schedule of reinforcement. is it a FR,VI,VR,FI