A Pigeon Trained on a MULT VI 60-S EXT 60-S

Multiple Choice

A pigeon trained on a MULT VI 60-s EXT 60-s schedule in which the VI schedule is signaled with a red light and extinction is signaled with a green light is not showing the development of any kind of stimulus discrimination. Which of the following might be a reason for this?

A) Superstition due to pecks that occur near the end of the EXT component
B) Positive contrast with the VI schedule
C) Negative contrast with the VI schedule
D) Retroactive interference with the VI schedule