Something about the two shapes in A is exchanged in B, while they stay where they are. Exchange the same thing in C.

In A the circle is big and the square is small; in B the circle is small and the square is big, each in its old place. So in C the triangle becomes small and the star becomes big, without moving: (c). (b) swaps the positions instead, (a) makes both small and (d) makes both big.