In the traditional Japanese household, most clothing could be packed flatly, and so it was not necessary to have elaborate closet facilities.
(A) flatly, and so it was not necessary to have elaborate closet facilities
(B) flat, and so elaborate closet facilities were unnecessary
(C) flatly, and so there was no necessity for elaborate closet facilities
(D) flat, there being no necessity for elaborate closet facilities
(E) flatly, as no elaborate closet facilities were necessary

My doubt is how we decide between "flat" and "flatly"...What are they in this sentence?? I mean adverb or what..i personally feel that
packed is verb so flatly is an adverb...but not sure...OA after some discussion