题目

等比数列{an}中，a2＝9，a5＝243，则{an}的前4项和为(    ). A．81         B．120          C．168       D．192 答案：B—I have a toothache.           —                     . [     ]A. It doesn’t matter      B. You should see a dentistC. You should drink lots of water    D. What’s the matter with you?