The correct answer is c.: it served as the be boundary between North Korea and South Korea. The current line is in a similar place, but it's not a straight line, unlike the line running along the 39th parallel.
The next capital would be Lima, Peru
some of the Incas used camels/lamas to transport the trade across their dirt road is you look on google maps you can see their roads
One thing is the power of it if its faster it erodes more if its slower doesn't really erode anything
i don't know the other two things but hope this will help you