I also agree that it is B
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.
