In each wheel some of the eight parts are shaded. Find how many are shaded and where the shading starts, then choose the next wheel.

The shaded block grows by one part each time (1, 2, 3 parts) and each new block starts just clockwise of where the last block ended. The last block ended at the part left of the bottom, so four parts are shaded, from the upper-left part over the top to the part just above the right-hand side: (a). (c) shades only three parts and (b) and (d) start in the wrong place.