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一、等差数列选择题*1.在数列an中,a129,an1an3nN>>>>>>>>>>>>>>>>>>>>>>>>,则a1a2>>>>>>>>a20>>>>()A.10C.300B.145D.3202.等差数列an中,a22,公差d2,则S10=()A.200B.100C.90D.803.等差数列an中,已知a1a4a739,则a4()A.13B.14C.15D.164.设Sn是等差数列an的前n项和.若a1a4a76,则S7()A.10B.8C.12D.145.已知等差数列{an}的前n项和为Sn,则下列判断错误的是()A.S