Using a river as a boundary (border) may be a poor choice because:

select one:
a. rivers tend to bring people together rather than separate groups of people
b. the course of a river can change leading to a land dispute
c. rivers do not follow straight lines are difficult to map
d. all of the above
e. both a and b above

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

[Yes]

b. The course of a river can change leading to a land dispute

[Yes, but the direction of river flow should not change its location, and so the border will remain the same.]

c. Rivers do not follow straight lines are difficult to map

[Yes]

d. All of the above

e. Both A and B above

answer is i don't know