Professor Lee is considering going to teach in Shenzhen, where he can get paid . A.as five times much B.as much five times C.much as five times D.five times as much 答案:D已知:如图所示的一张矩形纸片,将纸片折叠一次,使点与重合,再展开,折痕交边 于,交边于,分别连接和. (1)求证:四边形是菱形. (2)若,△的面积为,求△的周长. (3)在线段上是否存在一点,使得?若存在,请说明点的位置,并予以证明;若不存在,请说明理由.