For protection from thesummer sun,the Mojave lived in open-sided,flat-topped dwellings known as shades,each a roof of poles and arrowweed supported by posts set in a rectangle.

A. each a roof of poles and arrowweed

B. each a roof of poles and arrowweed that are being

C. with each being a roof of poles and arrowweed

D. with roofs of poles and arrowweed to be

E. with roofs of poles and arrowweed that are

答案选A，想不通，我选了E，题目意思都不太明白，请各位大侠帮忙看看