On an AO part-fitting question, the answer choices all show the same two shapes but in different orientations. The shapes have one straight edge and one curved edge each. What confirms the correct fitting?

CURVED EDGE MATCHING is the most distinctive visual feature in many AO part-fitting questions because curved edges have a single correct orientation for a perfect fit.

The convex-concave rule: For two pieces with complementary curved edges to fit perfectly, the curve on one piece must be the exact mirror image of the curve on the other — a convex bulge fits into a concave depression of the same radius and shape.

Checking fit: Visually trace the curved edge of one piece; the matching edge of the other piece should trace the identical path in reverse; if the curves have different radii, different profiles, or the same direction (both convex or both concave), they cannot fit.

Combined outline check: If the question shows a target shape that the assembly should produce, check whether the assembled pieces would create that outline — this gives a second verification method.

Rotation check: Curved edges are not symmetric under all rotations — a piece may need to be rotated 180 degrees to present its concave side to the matching convex side.

Practice tip: Practice with actual curved puzzle pieces; this physical experience of feeling convex and concave pieces fit together builds the spatial intuition that translates directly to visual AO questions.