Frasier Was on a Bridge,planning to Commit Suicide

Frasier was on a bridge,planning to commit suicide.On one side of the bridge,about 40 people stood and pointed at him as he clung to the railing.On the other side of the bridge,a lone onlooker saw him,and immediately called for help.Why was the lone person more likely to help than any individual in the crowd

A)  Cognitive dissonance decreases as the size of a group is decreased. 
B)  Group polarization is less likely to occur in small groups. 
C)  Diffusion of responsibility is less likely to occur in a small group. 
D)  Small groups tend to be less cohesive than larger groups.