Topic: Adverb (ক্রিয়াবিশেষণ),

Best Answer Explained in Below-:

In the phrase "The sun went 'down'," the word "down" functions as an adverb. Adverbs are words that typically modify verbs, adjectives, or other adverbs, providing additional context such as how, when, where, or to what extent an action is performed. In this case, "down" modifies the verb "went," indicating the direction of the action. When we say "the sun went down," we are describing the downward movement of the sun in the sky, which is a crucial aspect of understanding the action taking place.

If "down" were an adverb, it would generally come in forms like "he ran quickly," where "quickly" modifies the verb "ran." However, in the provided example, "down" provides a specific spatial context that enhances our understanding of the verb "went." The other options—preposition, noun, and conjunction—do not apply here. A preposition would link a noun to another element in the sentence (e.g., in, on, at), a noun represents a person, place, thing, or idea (e.g., sun, book), and a conjunction connects clauses or sentences (e.g., and, but). Hence, option B, "adverb," is the correct answer.