More parts of wheel A are shaded to give wheel B. Shade more parts of wheel C by the same rule. Which wheel do you get?

Every shaded part of A stays shaded in B, and the part just after it going clockwise is shaded as well, so each single part grows into a pair. In C the two neighbouring parts on the right become three, and the part on the upper left gains its clockwise neighbour at the top: (a). (b) adds the anticlockwise neighbours, (c) moves the parts round without keeping them and (d) shades the parts that were white.