The green flash, an atmospheric refractive phenomenon whereby the top

KAPLAN OFFICIAL EXPLANATION

STEP 1: READ THE ORIGINAL SENTENCE CAREFULLY, LOOKING FOR ERRORS
The GMAT prefers concise constructions. This underlined piece sounds awkward. Moreover, -ing constructions such as “of requiring” are generally suspect on the GMAT. Seek an answer choice that is less wordy and that removes the phrase “of requiring.”

STEP 2: SCAN AND GROUP THE ANSWER CHOICES
(A) and (B) keep “on account of.” (C), (D), and (E) all use “because.”

STEP 3: ELIMINATE CHOICES UNTIL ONLY ONE REMAINS
“Because” is certainly shorter and more concise than “on account of,” so eliminate (A) and (B). (C) uses the pronoun “they,” but it refers to the “green flash,” so the pronoun should be singular. Hence, (C) cannot be correct. (D) uses the pronoun “it,” which agrees with its antecedent, the “green flash.” This choice is concise and grammatically correct and is thus the correct answer. (E) is incorrect because it uses the phrase “of requiring,” which sounds awkward in the original sentence. (D) is the correct answer. Read it back into the sentence to confirm: The green flash, an atmospheric refractive phenomenon whereby the top edge of a setting sun will momentarily turn green, rarely is seen by the naked eye, primarily because it requires specific favorable conditions to occur.