Here's why:
* Prepositions show the relationship between a noun or pronoun and another word in the sentence. They often indicate location, direction, time, or manner.
* Until is a conjunction that indicates a time limit. It joins two clauses, showing that one action will continue "up to the time that" the other action happens.
Examples:
* Prepositions: I walked along the river. She waited beyond the gate.
* Conjunction: I will wait here until you return.