求助一题----我也不知这题出自哪

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.

1. Columbus was the Incan highway, which, over 2,500 miles long and extending
2. Columbus was the Incan highway, over 2,500 miles in length, and extended
3. Columbus, the Incan highway, which was over 2,500 miles in length and extended
4. Columbus, the Incan highway, being over 2,500 miles in length, was extended
5. Columbus, the Incan highway was over 2,500 miles long, extending

   Answer: E

我选的是A，其实我也觉得A很别扭，但是E明显缺谓语啊，主语又究竟是哪个。

哪位大虾能不能告诉我下各个选项都对在哪错在哪 ，不胜感激！

系动词就是was啊

前面一长句是同位语，主语是Incan highway