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

In this figure-formation reasoning type, a target shape is cut into a small number of regions by straight lines, and each candidate piece must match exactly one region by its number of sides, its angle character (acute, obtuse, or right), and its relative size. A piece carrying a feature the target's cut lines can never create, such as a right angle or a pair of parallel sides, is eliminated immediately without testing the full assembly.

The equilateral triangle in the solution figure is divided by two lines drawn from one interior point, one to the top vertex and one to a point on the base and on to the bottom-right vertex, producing exactly three regions: a large triangular region on the right side, a small triangular region near the base, and a four-sided region on the left side.

1. Figure (3), a scalene, obtuse-angled triangle, fits the large triangular region on the right side.

2. Figure (4), a small, narrow triangle, fits the small triangular region near the base.

3. Figure (5), a slanted four-sided figure, fits the remaining region on the left side.

Checking the two rejected figures against the same three regions confirms no other set of three pieces can work:

• Figure (1) is a right-angled triangle. Neither cut line meets the triangle's sides at a right angle, so none of the three regions carries a 90-degree corner, and figure (1) cannot replace any of the matched pieces.

• Figure (2) is a trapezoid, that is, it has a pair of parallel sides. The four-sided region on the left is a general quadrilateral with no parallel sides, so figure (2) cannot replace figure (5) there either.

Since figures (3), (4), and (5) are the only three pieces that reproduce all three regions exactly, with no gap or overlap, option 345 is correct.