A hungry pigeon is in a Skinner box and is pecking a key for access to food. The first food delivery occurs for the first peck after 1 minute has elapsed. The second occurs for the first peck after 3 minutes has elapsed. The third food delivery occurs for the first peck after 2 minutes has elapsed. All other pecks went unrewarded, but the pigeon did not receive access to food unless it pecked the key. The pigeon is most likely on a _____ schedule of reinforcement.
FR
VR
FI
VI