题目

--Can your sister swim? --                  ． A．Yes, she does                   B．No, she can't C．Yes, she can't                   D．No, she can 答案：B（2009安徽卷理）（本小题满分13分）如图，四棱锥F－ABCD的底面ABCD是菱形，其对角线AC=2，BD=，AE、CF都与平面ABCD垂直，AE=1，CF=2.（I）求二面角B－AF－D的大小；（II）求四棱锥E－ABCD与四棱锥F－ABCD公共部分的体积.