The green flash, an atmospheric refractive phenomenon whereby the top : Sentence Correction (SC)

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 on account of requiring specific favorable conditions to occur.

(A) on account of requiring
(B) on account of their requiring
(C) because they require
(D) because it requires
(E) because of requiring