Which of the following is NOT a disadvantage of an oligarchy? Oppressed voices Oppressed citizens Using helots to fight wars Lack of new ideas

Using helots to fight wars is not a disadvantage of an oligarchy *itself*. Helots were a specific class of unfree laborers in ancient Sparta, which was an oligarchy. While Sparta's use of helots was related to their social and political structure, it's not a universal characteristic of oligarchies. The other options, oppressed voices, oppressed citizens, and lack of new ideas, are common disadvantages found in oligarchical systems where power is concentrated in the hands of a few.