Using a river as a boundary (border) may be a poor choice because:
[Editor's Comment: Use process of elimination!]
Select one:
a. Rivers tend to bring people together rather than separate groups of people
<em>[Yes]</em>
b. The course of a river can change leading to a land dispute
<em>[Yes, but the direction of river flow should not change its location, and so the border will remain the same.]</em>
c. Rivers do not follow straight lines are difficult to map
<em>[Yes]</em>
d. All of the above
e. Both A and B above
