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

Concept: In a figure-dissection (assembling) reasoning question, one whole figure is cut into a few pieces along straight-edged cut paths - a cut path may run straight from one boundary point to another, or bend at an interior vertex into two straight segments. Each answer figure is EITHER one such actual piece, shown after only being rotated (never mirrored) from its position in the original, OR a distractor outline that the cuts do not actually produce. Solving it means matching each candidate outline - its number of vertices, its straight edges, and any inward (concave) notch or outward (convex) step created where a cut path bends - against the pieces the cuts actually produce, not judging by a figure's general look or its position among the choices.

Application: The image shows an equilateral triangle cut by two lines running from its top vertex down to the base; one of these two lines is not straight - it steps sideways partway down, so where it meets its neighbouring piece the boundary is not a plain straight edge. That single dissection produces three separate pieces: a plain three-sided piece with no notch, bounded by the triangle's own left side, the base, and one straight interior cut line; a piece whose boundary is indented by a concave notch at the point where the stepped line cuts into it; and a second piece on the other side of that same stepped line, whose boundary instead juts outward with a matching convex step at exactly that point - the two interlock along the shared bend, since both are produced by the same cut. Rotating each candidate figure to compare: figure 2 is a clean, notch-free triangular outline, which matches the plain first piece. Figures 4 and 5 both carry a single step in their outline at a similar relative position - one reading as an inward notch, the other as an outward jog - consistent with the two pieces produced along that shared bent cut line. Figures 1 and 3 do not reproduce this specific step: figure 1's outline is essentially convex end-to-end with no interlocking step, and figure 3's step sits close to its longest edge rather than at the same relative position as the dissection's bend, so neither can close the triangle without leaving a gap or an overlap. Fitting 2, 4, and 5 together - the plain piece, then the two stepped pieces interlocking along their shared boundary - reconstructs the full equilateral triangle.

Cross-check: As a check, trace the assembled outline: the three original sides of the triangle (contributed once each by the pieces that carry them) and the two interior cut lines (each traced twice, once by each neighbouring piece) close up with no leftover edge and the triangle's three 60-degree corners intact - confirming figures 2, 4, and 5 are the correct set.