What Is the Primary Distinction Between an Oligarchy and a Democracy

What is the primary distinction between an oligarchy and a democracy?

A) In an oligarchy, religious figures have greater control, whereas a democracy is ruled by the upper class.
B) In an oligarchy, one single person has control over all functions of government, whereas that power is distributed in a democracy.
C) In an oligarchy, a royal family has control over the governing system, while religious institutions have control in a democracy.
D) In an oligarchy, a select class of people hold most of the power, whereas all citizens hold power in a democracy.