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

Concept: In a figure-fitting series, the printed square already shows the exact boundary lines that the correct pieces must trace; a valid combination of three pieces must together reproduce every printed division line with matching edge lengths and vertex angles, leaving no gap and no overlap anywhere inside the square.

Application: The square's own outline is broken by one large stepped boundary running from the top edge across to a side, plus two thin triangular corners left open. Among the loose pieces, only the shape with a step of exactly that size and angle (piece 3) reproduces the large stepped boundary; the two remaining narrow slivers (pieces 4 and 5), each a slim triangle with a long diagonal edge, exactly match the two triangular corners still uncovered.

Cross-check: Swapping piece 3 for the similarly shaped stepped piece 2 shifts the step off the square's printed line and opens a visible gap along one edge, so 2 cannot substitute for 3; and the remaining pointed piece (piece 1) has a vertex angle that does not match either uncovered triangular corner, confirming the corners can only be closed by pieces 4 and 5.

Result: Fitting pieces 3, 4 and 5 edge-to-edge therefore reconstructs the complete square with no gap or overlap -- the combination 3-4-5.

Why the other combinations fail:

• 123 -- piece 1's blunt, rounded vertex meets piece 2's differently-angled step at mismatched edges, so 1, 2 and 3 leave a gap where 1 and 2 meet.

• 234 -- pieces 2 and 3 are both stepped shapes cut at different positions, so together they misalign the stepped region rather than tracing it once; adding piece 4 does not fix this, so 2, 3 and 4 cannot form the square.

• 134 -- piece 1's blunt vertex cannot align with piece 4's sharply-angled diagonal edge, so 1, 3 and 4 leave a mismatched edge and cannot form the square.

• 345 -- pieces 3, 4 and 5 fit together edge-to-edge with matching lengths and angles, exactly reconstructing the square with no gap or overlap.