With Regard to the Bystander Effect, What Has Been Suggested

With regard to the bystander effect, what has been suggested as the most likely factor increasing the ambiguity of the situation?

A) the inability of the victim to explain what has happened
B) the presence of other witnesses who do not respond
C) the characteristics of the victim
D) a steady diet of television violence
E) the person needing help is not from the bystander's own ethnic group