Concept:A system where only one political party is legally allowed to exist is known as a de jure one-party system.
Explanation:The key word in the question is “legalized.”
This means the existence of a single party is formally recognized and enforced by the constitution or law.
When a single party is legally permitted to form the government, it is called a de jure one-party system.
In contrast, a de facto one-party system occurs when one party dominates in practice, even though other parties are legally allowed.
A totalitarian single-party system and a mass party system do not specifically describe the legal monopoly of a single party.
Answer:A. de jure one-party system