There are two algorithms for the area of this graph:

One is to divide it into upper and lower rectangles, so its area is a1(b1-b2)+(a1+a2) b2;

One is to divide it into two rectangles. Then its area is A 1b 1+A2B2. So a1b1+a2b2 = a1(b1-b2)+(a1+a2).

So choose C.