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 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

Answer: I would contend that the right answer is the E) "Columbus, the Incan highway was over 2,500 miles long, extending ... "

Explanation: Just to elaborate a little on the answer, it can be added that it is not very formal to use the word "being," so option D should be easily discarded. In addition, in option C the use of "which" seems redundant, since the sentence is already about the Incan highway. Furthermore, option B is also incorrect, since the sentence should say "extending" and not "extended" (it extended that distance, but it was not extended). Finally, option A can also be discarded, since "which" should have been followed by a verb. Option E is, therefore, the correct one, since the first sentence acts as a definition of the Incan highway, which is subsequently described in further detail.