While aggression may in certain circumstances be appropriate (perhaps in a competitive situation), we generally cannot be lashing out at others in most social situations. What is the name of the mechanism for curbing aggressive tendencies?

What resource must we typically draw on to curb those tendencies? Describe the "donut" study used to test this hypothesis?
What will be an ideal response?

Answer:
Self-regulation is the name of the mechanism for controlling aggressive urges, and such self-control appears to require cognitive resources.
In one study, participants were given either a delicious donut or a radish but were not allowed to eat either one. Then participants got annoying negative feedback from "another participant" (who didn't really exist) on an essay they had written. Participants were then asked to prepare a snack for the other participant; they were allowed to put as much or as little hot sauce on the snack--after having been told that the other participant didn't like spicy dishes, thus, more hot sauce equaled more aggression. Participants who had been exposed to the donut used more hot sauce on the snack. This showed that cognitive resources were used up while earlier resisting the donut, but not the radish. Thus people whose cognitive resources are depleted, perhaps even by lack of good sleep, may be more inclined to aggress against others.