Select the figure from among the given options that can replace the question mark (?) in the following series.

Correct — B. Two stacks grow, but never in the same step.

Rule: one arc is added per box, and the two corners take turns — bottom-left going first.

Top-right arches: 1, 1, 2, 2 → 3 (its turn)
Bottom-left cups: 1, 2, 2, 3 → 3 (unchanged)

Box 4 already added a cup, so box 5 must add an arch. Option (b) shows three arches at the top right and three cups at the bottom left.

Why the others are wrong

• (a)
  A third corner appears. Option (a) drops both stacks back to two and adds a cup at the bottom right, a corner the series never uses.
• (c)
  The wrong stack grows. Option (c) leaves the arches at two and pushes the cups to four, adding to the corner that already took its turn at box 4.
• (d)
  Two arcs added at once. Option (d) has the right cup count but jumps the arches from two to four, where one arc per step is the rule throughout.

This is a counting series dressed up as a picture. The arcs never move, rotate or change shape — only how many are stacked in each corner changes.

The pattern is an alternating increment: the total rises by exactly one arc per box, and the two corners take that increase in turn.

So the pair of counts walks 1-1, 1-2, 2-2, 2-3, 3-3 — a staircase in which each step raises one number and holds the other. Knowing which corner moved last tells you which moves next.

Key facts

• The counts run 1-1, 1-2, 2-2, 2-3, so the fifth box must be 3-3.
• The total number of arcs rises by exactly one per box, from 2 in the first box to 6 in the fifth.
• Top-right arcs open downward and bottom-left arcs open upward throughout, so orientation is not part of the pattern.

Common traps

• Adding one to both corners at once and hunting for a 3-4 figure.
• Missing that box 4 raised the cups, and raising them again instead of the arches.
• Reading the two faint arcs of box 3 as one, and losing the count from there on.

No directly related past PYQ was found.