They climbed to the top of the tower, _____ they could see _____ was happening in the distance. A. where, all what B. from where, what C. which, all D. from which, that 答案:B如图1,平面直角坐标系中有一矩形纸片OABC,O为原点,点A、C分别在x轴、y轴上,点B的坐标为(,1),在BC边上选取适当的点D,将△OCD沿OD翻折,点C落在点E处,得到△OED.(1)若点E与点A、点B构成等腰三角形,求点E的坐标;(2)若点E在一次函数y=2x-1的图象上(如图2),求点D的坐标;(3)当线段OD与直线EA垂直时(如图3),求△CDE的外接圆的半径.