Shannon Is Walking Down the Street with a Friend One

Shannon is walking down the street with a friend one day when a stranger up ahead suddenly shouts "Get back! Get off the street! There's a sniper!" Shannon and her friend are most likely to obey if

A) the stranger looks very frightened.
B) the stranger is a police officer.
C) they have low psychological resistance.
D) the friend is over the age of 30 years.