If a line makes an angle of $30^{\circ}$ with the positive direction of x-axis, $120^{\circ}$ with the positive direction of y-axis, then the angle which it makes with the positive direction of z-axis is : (A) $90^{\circ}$ (B) $120^{\circ}$ (C) $60^{\circ}$ (D) $0^{\circ}$