题目

已知｛an｝是等比数列，且an＞0，a2a4+2a3a5+a4a6=25,那么a3+a5的值为A.5                              B.10                             C.15                                   D.20 答案：解析:∵a2a4=a32,a4·a6=a52，∴(a3+a5)2=25.又an＞0，∴a3+a5=5.答案:A The children, _____ had played the whole day long, were worn out.      A. all of what                                             B. all of them      C. all of whom                                           D. all of which