求问一道题：GWD第一套3题

3.For protection from the summer sun, theMojave lived in open-sided, flate-topped dwelling know as shades, each aroof of poles and arrowweed supported by posts set in a rectangle.

A.     eacha roof of poles and arrowweed

B.     eacha roof of poles and arrowweed that are being

C.     witheach being a roof of poles and arowweed

D.     withroofs of poles and arrowweed to be

E.      withroofs of poles and arrowweed that are

这题什么意思？为了隔离夏天的太阳，M住进开着门的、平顶的住宅，每一个房顶的尽头和杂草都被矩形的装置支撑着。

答案是A。为什么不选E？

谢谢！