In the scene, the upper structure has a missing piece outlined with a dashed line. There are 4 candidate pieces below. Sequentially check each candidate from left to right: highlight the current candidate being examined with a frame, preview how the piece fits in the gap, then judge it: if the shape matches, turn its box green and mark it with a green ✓; if it doesn't match, turn its box red and mark it with a red ✗. Then move to the next candidate. Once the matching piece is found, output 1 image showing it moved into the gap to complete the structure. Only modify what the task requires; keep the background and any other element unchanged.