Bill Spends His Summer in the City Panhandling

Bill spends his summer in the city panhandling.Every day he takes a position on a busy corner and accosts passersby saying, "Can you spare some change?" Most people ignore him, but every now and then someone gives him money.Bill's reinforcement schedule is best described as a .

A) fixed ratio schedule
B) variable ratio schedule
C) fixed interval schedule
D) variable interval schedule