Look for pieces with an opposite edge matching the edge of a piece already
placed.
For example, the bottom edge of D4 should match the top edge of E4. The piece
must be among the pieces shown for row D (D1, D2, or D10) or for column 4 (B4,
J4, or K4). Looking at those pieces, only D1 has a good match along its bottom
edge.

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