题目

---- Is there anyone here      name isBetty? ---- Sorry, I don’t know. A. who    B. which      C. whom   D. whose 答案：D5．设正项等差数列{an}的前n项和为Sn，已知S5=40，且a4，a8-1，a15成等比数列，则S15等于（　　）A．225B．345C．350D．535