The correct option is D.
Oligarchy refers to the type of government in which the power structure is vested in just a few number of individuals. This form of government is also know as 'Government by the few'. The few people, who hold the rein of power in this type of government are usually motivated by selfish purposes. This type of government always oppress the citizens in order to ensure that they are subject to all his rules and regulations. The ruling individuals are usually set apart from the ordinary citizens by mean of their wealth, social class, prestige, kinship, economic status, etc.