第16～25小题．要求判断每题给出的条件(1)和(2)能否充分支持题干所陈述的结论．A、B、C、D、E五个选项为判断结果，请选择一项符合试题要求的判断．
A．条件(1)充分，但条件(2)不充分．
B．条件(2)充分，但条件(1)不充分．
C．条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．
D．条件(1)充分，条件(2)也充分．
E．条件(1)和(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．
a1a8＜a4a5．
(1) {an}为等差数列，且a1＞0
(2) {an}为等差数列，且公差d≠0
参考答案：B
解析：
[解] 由条件(1)，设数列公差为d，则
所以，a1a8-a4a5=-12d2≤0，但当d=0时，推不出a1a8＜a4a5，条件(1)不充分．
由条件(2)，仍可得a1a8-a4a5=-12d2，又d≠0，可得a1a8-a4a5＜0，条件(2)充分．
故本题应选B．
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