A small flag changes position and colour along the series. Which figure should come in place of the question mark?

Two rules act together: the flag turns $45^{\circ }$ clockwise each step, and it is alternately filled and empty. The last flag is empty, so the next one is filled and turned another $45^{\circ }$: pole upright, flag at the bottom pointing left — (c). (a) forgets the colour change, (b) turns $90^{\circ }$ and (d) is a mirror image, not a turn.