Question

Which option shows articles and modifiers being used​ correctly? A. She lives on an twentieth floor of the old apartment building somewhere in Manhattan. B. She lives on the twentieth floor of a old apartment building somewhere in Manhattan. C. She lives on the twentieth floor of an old apartment building somewhere in Manhattan. D. She lives on a twentieth floor of the old apartment building somewhere in Manhattan.

Answer 1

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)