题目

---What’s wrong with you ? You look so tired.       --- Last night I ________ sleep well.       A. couldn’t         B. can’t          C. wouldn’t 答案：A在等比数列{an}中，a9+a10=a(a≠0),a19+a20=b,则a99+a100等于(    )A.           B.()9           C.          D.()10