ANS:A - rn

Its just like error at nth station =n*e/N in link traverse.

Here, a probable error at initial=0, similarly at the end is r√(n).

At middle would be averagei .e=r* √(n)/2. I think;

r = error in one link.
n = total no of links.
Initial error = 0.
Error at end = r√n,
Error at middle = avg.
= (0 + r√n) 2
= r√n.