C I believe.........................
The biological basis of behavior
It would be D. The bystander effect. It takes some time before anyone helps because they might assume he will get up on his own ok, that someone else will help, or maybe didn't see what happen and are waiting for someone else to take control. The more people their are, the more likely this is to happen. It's not really our fault, it's just something we do in a unexpected situation. :)
