Which of the following is NOT a correlative conjunction?

The correct answer is C, "Unless," because it does not function as a correlative conjunction. Correlative conjunctions are pairs of conjunctions that work together to connect equal elements in a sentence, and they typically include words such as "both-and," "either-or," and "neither-nor."

"Both-and" is used to connect two positive statements or items, indicating that each part is included. "Either-or" is used to present two alternatives, indicating that one of the two choices must be selected. Similarly, "neither-nor" connects two negative statements, confirming that neither option holds true.

In contrast, "Unless" functions as a subordinating conjunction rather than a correlative one. It introduces a condition that negates the main clause, essentially translating to "if not." Therefore, it does not operate in the paired structure characteristic of correlative conjunctions, making it the correct response to the question.