题目

 — Was there a computer in your study?    — ______  A. Yes, there is.                    B. No, there isn’t.     C. Yes, there was.                  D. No, there was. 答案：C设二次函数y=x2-2x-3与x轴的交点为A，B，其顶点坐标为C，则△ABC的面积为 ．