Question

a small group of people - usually military officers - who rule a country after taking it over by force

Explanation:

The definition given is of a small group (often military officers) that seizes power by force to rule a country. "Junta" specifically refers to such a group. "Oligarchy" is rule by a small elite (not necessarily via forceful takeover), "democracy" is rule by the people, and "dictatorship" is rule by a single dictator, so "junta" matches the definition.

Answer:

A. junta