— Are those your friends?
— No, ___________. They are my cousins.
A:he is
B:those aren't
C:he isn't
D:they aren't.
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已知数列{an}的前n项和为Sn,且Sn+1=2an,则使不等式a12+a22+…+an2<5×2n+1成立的n的最大值为____