单选题设区域D是由直线y=x，x=2，y=1围成的封闭平面图形，<br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20240620/14288017_0.png"><br/> <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20240620/14288017_0_1.png">