"avoid promising more than you can deliver" is a suggested guideline for using power.

The correct answer is reward.
Reward power refers to people with authority who can reward others (usually those working for them) for doing something. These rewards can be either material or intangible, but they have to be given - the leader giving them out cannot promise a reward that he or she cannot give. This system is good for leaders who want to motivate their employees to act.