The correct answer is A. Rule by a small, often self-selected group.
Explanation
An oligarchy is a form of government in which political power is held by a select group generally of the same social class. According to the ancient Greeks, the oligarchy is the degradation of the aristocratic system in which the individuals that were the best prepared for this function govern, however, in the case of the oligarchy the mandate can be inherited in a family or selected based on religion, causing that the rulers are not chosen based on their own merits. So, the correct answer is A. Rule by small, often self-selected group.