题目

—When did you manage to get it completed?        —Not until a new technique was _________.        A. presented                 B. contributed               C. devoted                    D. introduced 答案：D判断下列两个结论：①正三角形是轴对称图形；②正三角形是中心对称图形．结果是（ ）A．①②都正确B．①②都错误C．①正确，②错误D．①错误，②正确