According to the Text, Why Was There a Difference Between

According to the text, why was there a difference between the results of Darley and Latané's laboratory research and Piliavin's field experiment?

A) in the Piliavin study, the victim was in full view
B) the natural groups were considerably larger than the laboratory groups
C) it was much more difficult for the participants in the Piliavin study to leave the area than it was for participants in the Latané and Darley studies
D) all of the above
E) none of the above