In a visual model, two strips of width n are subtracted from a square of side m and the corner n² part is added back. Which identity is formed?

Correct answer: (m−n)² = m²−2mn+n²

The direct answer is A. Begin with the large square of area m². Each strip has area mn, and two strips are removed, so subtract 2mn. The corner square of area n² is included in both strips and was therefore subtracted twice; adding it back once corrects the double subtraction. The result is m²−2mn+n², which equals (m−n)². Option A follows the exact remove-and-restore process. Option B adds the strips and describes enlargement by n, not subtraction. Option C is the difference-of-squares identity and has no +n² correction term. Option D is false in general because (m+n)² also contains 2mn. Memory cue: subtract two strips, then add the overlapped corner once.