In which visual model are the two middle rectangles equal to \(ab\) and \(ab\)?

Correct answer: \((a+b)^2\)

Direct answer: option C, \((a+b)^2\). In the area model, split both sides of a square of side \(a+b\) into lengths \(a\) and \(b\). This creates an \(a\) by \(a\) square of area \(a^2\), two rectangles measuring \(a\) by \(b\), each with area \(ab\), and a \(b\) by \(b\) square of area \(b^2\). Therefore, the total area is \(a^2+ab+ab+b^2=a^2+2ab+b^2=(a+b)^2\). Option A and option B describe the difference-of-squares arrangement; their total expression is \(a^2-b^2\), not a square with two positive middle rectangles. Option D is only a length, not an area model with four parts. The key clue is the two positive equal rectangles: they produce the middle term \(+2ab\). Memory cue: “plus square” means \(a^2\), two \(ab\) rectangles, and \(b^2\).