If a fitting-parts question shows you 4 pieces and one of the answer choices shows an assembled figure made of only 3 visible regions, what should you conclude?

Critical rule: ALL pieces from the disassembled set must appear in the assembled answer; NO piece may overlap another or be hidden; NO gaps allowed inside the contour. If an answer shows fewer regions than disassembled pieces, then either: (a) Pieces are overlapping (not allowed); (b) Pieces are hidden somehow (not allowed in 2D AO); (c) Pieces are missing (not allowed); (d) The answer is genuinely just wrong. STRATEGY: count pieces in each answer choice. Each piece should be visible as a distinct region in the assembled figure (though edges between pieces may be subtle if they share long shared edges). The total visible regions should equal the number of disassembled pieces. EXCEPTIONS: sometimes two adjacent pieces have edges that line up exactly with each other and the shared boundary appears as a single line — but it's still TWO regions in the count. Look carefully for these subtle boundaries. COMMON WRONG ANSWERS: (1) An answer with fewer regions than disassembled pieces (one piece missing or hidden); (2) An answer with too many regions (extra piece added); (3) An answer where the regions are correctly counted but the shapes are altered (sides have changed length). After counting, verify each region matches a corresponding disassembled piece in shape and size. If the count matches but one region is the wrong shape, the answer is wrong. CONTOUR CHECK: the contour of the assembled figure is what you'd trace around the OUTSIDE of all the pieces fitted together. This contour should not have gaps inside (no holes) and should not have pieces sticking out unexpectedly. The contour should be one continuous closed shape. If an answer shows holes or has pieces seemingly floating apart, it's wrong. The pieces in AO are 2D and assembled flat (no stacking or 3D); the assembled figure is also 2D and flat.