which 定语从句, 如前面有逗号((( , which))))xinx形式,可以解释前面的word吗?而没有限制的作用,对马?
gwd6-41
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.
Columbus was the Incan highway, which, over 2,500 miles long and extending
Columbus was the Incan highway, over 2,500 miles in length, and extended
Columbus, the Incan highway, which was over 2,500 miles in length and extended
Columbus, the Incan highway, being over 2,500 miles in length, was extended
Columbus, the Incan highway was over 2,500 miles long, extending为什么C答案不好呢? | 
