Phoebe Saw the Passenger in the Seat Across the Aisle

Phoebe saw the passenger in the seat across the aisle suddenly slump forward in her seat.While the other passengers looked around for a flight attendant,Phoebe immediately started to administer CPR.What factor explains the absence of the bystander effect in this situation

A)  Passengers on a plane cannot be defined as a "group." 
B)  Phoebe perceived the other passenger to be in obvious physical danger. 
C)  Women are not vulnerable to the bystander effect. 
D)  There were so many people on the plane that the effect was diluted.