Identify the part of speech of the underlined word in the following sentence:
Sit down and rest awhile.

While' can function as various parts of speech (noun, conjunction, adverb, etc.).
The nature of the word can be found out through its position in the sentence.
- Option D:The given sentence ends with the word 'while'.
 A preposition usually precedes a noun and connects it with the rest of the sentence. Since this sentence ends with 'while', the word cannot be a preposition.
Hence D is not the right option.
- Option B: Similarly, adjectives also come before nouns that they modify. Since this word comes last, and also it does not modify any other word, option B is wrong.
- Option C: Adverbs modify verbs, adjectives and other adverbs. The word 'while' does not modify any of these parts of speech. Hence C is incorrect.
- Option A: 'While' refers to a 'period of time' in the given sentence. It functions as a noun as it names a 'period of time'. Nouns name things, here it names a certain amount of time.
Hence option A is correct.