If $z_1\:\:and\:\:z_2$ are non zero complex numbers such that $|z_1+z_2|=|z_1|+|z_2|$, then $arg z_1-arg z_2=?$

Question

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