题目

—We've only got this small bookcase. Will that do?—No, I am looking for is something much bigger and stronger. A . who B . that C . what D . which 答案：C如图，△ABC的三个顶点都在格点上，A（-1，3），B（-1，-1），C（-3，-3），（1）画出△ABC绕点A逆时针旋转90°所得图形△AB′C′；（2）直接写出△AB′C′外接圆的圆心D坐标________；（3）求∠AC′B′的正切值。