Concept: Discipline refers to self-control and the ability to follow rules or a code of behaviour.Explanation:Discipline involves training people to obey rules or a code of behaviour.It also means the capacity to control one's actions and impulses.This quality enables a person to behave in an orderly and controlled manner, even without external punishment.Therefore, among the given options, discipline is best described as the ability to behave in a controlled manner.Answer: D. ability to behave in a controlled manner