题目

平面直角坐标系中，四边形ABCD与四边形A′B′C′D′关于原点O位似，点A坐标为（﹣2，1），它的对应点A′（1，﹣0.5），如果AB=2，则A′B′= ． 答案：【1】1_______ several times, but he still doesn’t know how to do it properly. A. Being shown          B. Having shown him C. Having been shown                                             D. I’ve shown him