Problem 10-31(a) Vector electric field

The figure shows the positions of two a particles (charge on each is $+2e$) and an electron. What are the magnitude and direction of
(a) the resultant force on the electron?
(Hint: choose the $+x$ axis along the line from the electron to the right-hand a particle.)

[Ans.(a) $1.31 \times 10^{-8} N$ at $13.3^\circ$ to left of line from electron to right-hand a]

We are going to evaluate the force using components so we need to choose an $x, y$ coordinate system. There is no such thing as a "wrong" coordinate system but some are better than others because they simplify the solution. Which is best?

(A)

(B)

(C)

(D)