Piliavin, Rodin and Piliavin's Study Did Not Find Any Effect

Piliavin, Rodin and Piliavin's study did not find any effect for diffusion of responsibility, even though previous research had found this effect. What is the explanation for this?

A) The drunk victims were helped spontaneously less often
B) More people left the carriage the longer the emergency continued
C) Males were more likely to help than females
D) The participants were in an enclosed area and could see whether or not the victim was receiving help
E) The participants felt empathy for the victim