Under What Circumstances Are Bystanders Less Likely to Attempt to Help

Under what circumstances are bystanders less likely to attempt to help a stranger who appears to be in danger?

A) when the bystander could also be in danger
B) when there are lots of bystanders
C) when the danger comes from a natural, rather than a human, source
D) when the danger might lead to legal liability for a bystander who intervenes
E) when the source of the danger is a mugger or a rapist