This question tests grammatical knowledge specifically conjunctions. A conjunction is a word that connects clauses or sentences. 'Although' connects two contrasting ideas, establishing a complex sentence. Option A, B, and D are not correct. * **Core Concept:** Conjunctions * **Solution:** The correct answer is C because 'although' connects two clauses, thus functioning as a conjunction. Option A, B, and D represent incorrect parts of speech. * **Detailed Analysis:** * **A:** 'Although' does not name a person, place, or thing. * **B:** 'Although' doesn't show the relationship of a noun to another word, such as 'on', 'at', etc. * **C:** Correct. 'Although' joins two contrasting clauses together. * **D:** 'Although' doesn't modify a verb, adjective, or another adverb. * **Common Mistake:** Mistaking the function of connecting words or mixing up conjunctions with prepositions or other parts of speech.