Question

what distinguishes an oligarchy from a democracy?
the concentration of power in a small ruling group
the level of education possessed by the people
the size of the countrys population

Explanation:

Oligarchy is defined by power held by a small elite group, while democracy distributes power more broadly among citizens (e.g., through voting). Education level and population size are not core distinguishing features of these political systems.

Answer:

the concentration of power in a small ruling group