The use of "on account of" with a gerund ("requiring") is wordy and unidiomatic. The GMAT strongly prefers because over "on account of." Eliminate (A).
A quick scan of the beginnings of the choices reveals a 2-2-1 split, with (A) and (B) beginning with "on account of," (B) and (C) beginning with "because," and (E) beginning with "being that."
(A), (B), and (E) can be eliminated immediately. "Because" is the clearest, most concise connecting word that indicates the causation in the original sentence.
(D) uses "because of" instead of the more concise "because" and retains the gerund "requiring" from the original sentence. To be correct in front of "requiring," which here functions as a noun, the pronoun "it" would have to be the possessive its. But even if that change were made, this choice would be wordy and weak.
(C) is clear, concise, and correct.
Posted from my mobile device