The five-steps that are conceived by Darley and Latane refer to the five-steps of decision-making that the individual will go through in a situation where someone needs help. If all five-steps are undergone by the individual, than bystander effect will not occur and the person will provide her or his aid to the person in need. But if the individual stops at any one of these steps, he or she will not provide his or her aid and thus bystander effect will happen.
Thus the answer to the blank space is all.