Compare the three bars in each box with the bars in the box before it. What should the fourth box look like?

The orange middle bar never changes. The left bar grows by the same amount each time and the right bar shrinks by that amount, so after the bars are all level the left one becomes taller than the middle and the right one shorter: (c). (a) forgets to shrink the right bar, (b) changes the orange bar and (d) jumps two steps.