$Since the region is \textsl{below} the line $y=x-2$, the region must satisfy $y\leq x-2$, so the only options to consider now are (A) and (C). Note that the point $(x_0,y_0)=(3,0)$ lies in the region, and $y_0^2 = 0^2 = 0$, $4-x_0 = 4-3 = 1$, so $y_0^2 < 4-x_0$ (as $0<1$), so the region...