The correct answer is: Authority
Rationale: The essence of delegation is that the superior gives the subordinate part of his or her own authority.
Power is not conferred by the organisation, so it cannot be delegated: it must be possessed. The most important thing to note is that responsibility and accountability are not delegated: the superior makes the subordinate responsible and accountable to him for the authority he has delegated, but he remains responsible and accountable for it to his own boss.
Pitfalls: It is easy to confuse these concepts, which is why they would make an excellent exam question.