题目

数列{an}是等差数列，Sn是其前n项和，有且S7＜S8，S8=S9＞S10，则在下列结论中错误的是 A．a9=0         B．d＜0  C．S11＞S7                                   D．S8与S9均为Sn的最大值 答案：C10. I will tell David the good news at once when he comes back.(改为同义句)I will tell David the good news              he comes back.