In a 'fitting parts together' (jigsaw-type) problem, what must be true of the correct answer?

In a fitting-parts (puzzle/jigsaw) problem, you are shown several separate pieces and must pick the answer in which all of those pieces fit together exactly to form a complete shape — like assembling puzzle pieces. The correct answer uses every piece once, with no gaps between them, no overlapping, no extra pieces, and no piece resized or distorted. Wrong answers often add or omit a piece, change a piece's shape or size, or leave gaps. The strategy is to match each given piece by its edges and angles to its place in the assembled figure and reject any choice that alters or misuses a piece.