设D是xOy平面上以(1,1)、(-1,1)和(-1,-1)为顶点的三角形区域,D1是D在第一象限的部分,则等于( )。
A A.<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23817827_0_1.png"> B
B.<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23817827_0_2.png"> C
C.<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23817827_0_3.png"> D
D.0