If $z_1$ and $z_2$ are two non zero complex numbers such that $\mid z_1+z_2\mid=\mid z_1\mid+\mid z_2\mid$ then $arg(z_1)-arg(z_2)$ is equal to

Question

$\begin{array}{1 1}(A)\;-\pi&(B)\;\large\frac{\pi}{2}\\(C)\;\large\frac{-\pi}{2}&(D)\;0\end{array}$