As shown in the figure, charges `+q and -q` are placed at the vertices `B` and `C` of an isoscles triangle. The potential at the vertex `A` is
A. `(1)/(4pi epsilon_(0)).(2q)/(sqrt(a^(2) + b^(2))`
B. Zero
C. `(1)/(4pi epsilon_(0)).(q)/(sqrt(a^(2) + b^(2))`
D. `(1)/(4pi epsilon_(0)).((-q))/(sqrt(a^(2) + b^(2))`