A circle is cut into 8 equal parts and one part is shaded orange. Which figure continues the series?

The shaded part moves clockwise by 1, then 2, then 3, then 4 parts. The next move is 5 parts clockwise, from the part just below 3 o'clock round to the part just left of 12 o'clock: (c). (a) moves only 1, (d) moves 5 the wrong way and (b) repeats the move of 4.