题目

已知数列{an}的前n项和为Sn,且Sn=2(an-1),则a2等于A.4               B.2                C.1               D.-2 答案：答案：A  当n=1时，a1=2(a1-1),a1=2;当n=2时,a1+a2=2a2-2,a2=a1+2=4.

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