A wheel has eight equal parts. The orange part and the blue part move round the wheel at different speeds. Which wheel comes next?

The orange part moves one place clockwise each time; the blue part moves two places anticlockwise. From the last wheel, orange moves to the part just right of the bottom and blue moves two places back to the part just left of the bottom: (d). (a) leaves blue unmoved, (b) leaves orange unmoved and (c) swaps the colours.