A: over 2500 miles long and extending - it should be extends
B: extended (past tense) makes it sound like the road does not extend from ecuador to peru anymore
C: placing "the Incan highway" inside the commas means that it is additional information that does not need to be there for the sentence to make sense, but if you take it out the sentence makes no sense what so ever
D: same as C and changes meaning when it says "was extended"
E: Correct, removing phrases the sentence would read; The greatest road system built in the Americas, the Incan highway was over 2500 miles long, extending from northern Ecuador through Peru to southern chile