Linda sees a sign on a farmer's fence that reads: "HELP ME PICK STRAWBERRIES! FOR EVERY 5 QUARTS YOU PICK, KEEP ONE FOR YOURSELF." If Linda decides to pick strawberries for this farmer, she would be under a ________ schedule of reinforcement.
◦ fixed-interval
◦ primary
◦ variable-interval
◦ fixed-ratio
◦ variable-ratio