Select the option that can be used as a one-word substitute for the given…

Concept

A one-word substitution question asks for the single term that captures the meaning of an entire phrase. For government-type terms, the defining features are who holds power (one person, a small group, or the general population) and how that power is acquired (by inheritance, by appointment, or by election).

Application

The phrase "a government run by a king or queen" describes rule by a single hereditary head of state. The term matching this exact meaning is Monarchy — a system of governance headed by one ruler whose position is typically inherited.

Contrast

• Oligarchy: power is held collectively by a small group of people, not by one hereditary ruler.

• Republic: the head of state is elected or appointed, not inherited by birth.

• Democracy: power is vested in the people and exercised through elections, rather than concentrated in a hereditary ruler.

Therefore, the correct one-word substitute is Monarchy.