The answer is letter D.
None of the choices above exactly described what a manic episode is. It is not a disorder in and of itself but is a part of a type of bipolar disorder. Manic episodes usually last a period of one week where a person has an unusually irritable mood and is notably persistent in attaining goals presented to them. These episodes in mood disturbances are observable by others and can be compared to their usual state/behavior. If episodes occur very often they may impair overall functions of a person (e.g. work conditions, friendships, education).