885-sec3-16

16.   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（B）

(E) flatly, as no elaborate closet facilities were necessary

why flat, not flatly? thanks