Select three out of the following five alternative figures which together form a complete equilateral triangle.

Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → BCD
Pieces (B), (C) and (D) fit together to form the complete equilateral triangle, as shown below: the diamond (C) in the top corner, the small triangle (D) on the right, and the notched piece (B) along the base and the left side.

In the completed triangle the pieces are drawn to their exact shapes; the pieces printed in the paper are rough sketches of the same shapes, drawn at different sizes and slants.