[讨论]prep 2#187

186.       (32899-!-item-!-188;#058&007188)    (GWD-6-Q41)

The greatest road system built in the Americas prior to the arrival of Christopher Columbus was the Incan highway, which, over 2,500 miles long and extending from northern Ecuador through Peru to southern Chile.

A. Columbus was the Incan highway, which, over 2,500 miles long and extending 定于从句结构不完整

B. Columbus was the Incan highway, over 2,500 miles in length, and extended

C. Columbus, the Incan highway, which was over 2,500 miles in length and extended

D. Columbus, the Incan highway, being over 2,500 miles in length, was extended

E. Columbus, the Incan highway was over 2,500 miles long, extending

句子结构：The greatest road system built in the Americas prior to the arrival of Christopher Columbus, the Incan highway was over 2,500 miles long, extending from northern Ecuador through Peru to southern Chile.

主语同位语，S V O, doing  。doing 做was的伴随状语，

把B带进去：The greatest road system built in the Americas prior to the arrival of Christopher Columbus was the Incan highway, over 2,500 miles in length, and extended from northern Ecuador through Peru to southern Chile.

B为什么不对呢？