If $z_1$ and $z_2$ are two non-zero complex numbers such that $|z_1+z_2| = |z_1| + |z_2|$, then arg $z_1$ - arg $z_2$ is equal to :

Question

( A ) $\frac{-\pi}{2}$
( B ) $-\pi$
( C ) 0
( D ) $\frac{\pi}{2}$