请教GWD第一套第三题

Q3: For protection from the summer 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   ( Answer is A, each a  不语意重复吗？）

each引导的强调型独立主格结构。

强调句未的复数名词，

形式为：句子+复数名词结尾，each+介词短语/形容词短语/名词短语/-ing形式/-ed形式。

each的这种用法好像也是ETS prefer的。