Concept:The underlined word must be classified according to its function in the given sentence.
Explanation:In the sentence "Who came first in the race?", the word "first" modifies the verb "came".
It tells us the order or time in which the person arrived.
Words that modify a verb to show manner, time, place, or degree are called adverbs.
Therefore, "first" is used here as an adverb.
Now check the options:
A. Preposition – Incorrect, because prepositions show relationships like "in", "on", "at".
B. Adjective – Incorrect, because adjectives describe nouns, but "first" does not describe "who" or "race".
C. Adverb – Correct, because "first" describes the verb "came".
D. Article – Incorrect, because articles are only "a", "an", and "the".
Answer:C. Adverb