题目

Tom _______ Jack 1:0 at the 17th Tennis School Cup last night.   A. beated                                       B. beat   C. wined                                        D. won 答案： B  beat和win的过去式分别为beat和won，故排除A、C两项；beat后跟比赛的对手，win后跟比赛项目，由空格后的Jack可知选B。关于x的方程a2x2-（2a+1）x+1=0有实数根，则a满足的条件是    ．