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

Concept: In a "fit-the-pieces" figure question, the target shape can be split into a set of congruent unit pieces (here, small equilateral triangles obtained by joining the midpoints of the big triangle's sides). A group of three alternative figures reconstructs the target only if, together, they supply exactly this same set of unit pieces — same side length, same angles, no extra or missing area — so they interlock edge to edge with no gap and no overlap.

The target equilateral triangle splits into four such congruent smaller equilateral triangles, as shown below:

1. Figure (3) is a rhombus with 60°/120° angles — exactly two of the small equilateral-triangle units joined base to base, so it alone supplies two of the four triangular pieces needed.

2. Figure (1) and figure (2) are each a single small equilateral triangle, drawn rotated onto their side (pointing sideways) rather than upright — each supplies one more matching unit.

3. Together, (1) + (2) + (3) supply 1 + 1 + 2 = 4 congruent equilateral-triangle units of identical side length — exactly the number and shape into which the target triangle splits — so they interlock edge to edge with no gap or overlap to recreate it.

Cross-check — why the other figures cannot complete the set:

• Figure (4) is an irregular five-sided shape with unequal sides — its longest side over-runs the edge it would need to fill and its corners don't turn at 60°, so no trio built around it can close into the target triangle without a gap or overhang.

• Figure (5) is a trapezoid (only one pair of parallel sides, no 60° angle) — its parallel-sided profile cannot supply the 60° corner needed wherever it would sit, so no trio built around it closes into the target triangle either.

Only the trio (1) + (2) + (3) supplies exactly the four matching equilateral-triangle units with no leftover piece and no gap, so fitting these three figures together forms the equilateral triangle.