Which visual model clearly displays the four area parts of the identity a² + 2ab + b²?

Correct answer: A square with side (a + b)

Direct answer: A, a square with side (a + b). Divide each side of this square into lengths a and b. The resulting four regions are an a-by-a square with area a², two rectangles of dimensions a and b with areas ab and ab, and a b-by-b square with area b². Their total area is a² + ab + ab + b² = a² + 2ab + b². Therefore option A displays all four parts directly. Option B, the square with side (a − b), represents a² − 2ab + b², so its middle regions are associated with subtraction. Option C has area (a+b)(a−b) = a² − b² and therefore does not contain the 2ab term. Option D has area (ab)² and does not split into the required four regions. Memory cue: the plus square is the four-tile model with two positive ab rectangles.