Select the alternative which represents three out of the five alternative…

In a "form-the-shape-from-pieces" question, a candidate figure is a genuine piece only if its outline is an exact, undistorted copy of some region inside the target shape - the same number of straight edges, the same sequence of turns (including any inward, reflex fold), and the same relative edge lengths, with only its position and rotation changed. The method is to trace the lines that divide the target shape into its parts, note each part's edge-count and corner pattern, and match that fingerprint against every candidate figure.

Tracing the internal lines inside the square above shows it splits into exactly three four-sided regions: a large region running along the top and right edges that folds sharply inward at one interior point; a region along the left edge that closes into a four-sided kite shape with no inward fold; and a narrow four-sided sliver along the bottom that also folds sharply inward at its topmost point. Checking the five candidate figures the same way: figure (1) has four edges with one sharp inward fold and edge lengths matching the top-right region; figure (2) has four edges with no inward fold, matching the left-edge region; figure (5) has four edges with one sharp inward fold and edge lengths matching the bottom sliver. Rotated into place, figures (1), (2) and (5) dovetail exactly along every internal line, reconstructing the square with no gap or overlap.

The other two figures fail on a simpler ground - their own edge-count - before rotation even comes into it:

• Figure (3) is a plain triangle - only three straight edges. None of the square's three regions is bounded by three edges, so any combination built around figure (3) leaves a gap.

• Figure (4) has five straight edges (its small rectangular notch adds an extra corner). No region of the square has five edges either, so figure (4) cannot dovetail into the square no matter how it is turned.

Because figures (1), (2) and (5) are the only three whose edge-count, fold pattern, and proportions match the square's three regions piece-for-piece, they are the ones that fit together to form the complete square.