I believe it's an Indefinite pronoun. Hope this helps...
1. "...the sun hides in winter, peeking out only occasionally."
2. Alaska is beautiful, and special to the author.
<span>C. She lives on the twentieth floor of an old apartment building somewhere in Manhattan.
This option is accurate since it contains articles and modifiers that are grammatically correct:
i) "the" is used before the word "twentieth" (a noun modified by ordering- i.e. first, second, third, and so on...)
ii) "an" is used before the word "old" (which begins with a vowel)
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Benefits- easy to obtain, reliable. drawbacks - bad for environment, theres better alternatives.