The core concept here is the function of a conjunction in English grammar. * **Core concept:** A conjunction is a word that connects parts of a sentence. * **Correct Answer (C):** Option C precisely defines the function of a conjunction: to connect elements of a sentence (words, phrases, or clauses). Conjunctions facilitate smooth flow and logical relations between different parts of a sentence. * **Option A:** Describing a noun is the function of an adjective, not a conjunction. Adjectives modify nouns to provide descriptive details. * **Option B:** Expressing an action or state of being is the role of a verb. Verbs are central to the sentence, and are responsible for the action or status. * **Option D:** Showing the relationship between a noun and another word is the role of a preposition, not a conjunction. Prepositions define spatial or temporal relations. * **Key Takeaway:** Remember conjunctions are the glue of sentences, binding different elements together to form coherent thoughts.