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等差数列{an}的前n项和为Sn,S5=15,S9=18,在等比数列{bn}中,b3=a3...
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等差数列{a
n}的前n项和为S
n,S
5=15,S
9=18,在等比数列{b
n}中,b
3=a
3,b
5=a
5,则b
7的值为( )
A.3
B.2
C.
D.
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