问题
选择题
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答案
∵
=C n2n
，(2n)! n!(2n-n)!
=C n+12n+2
，(2n+2)! (n+1)!(n+1)!
∴
=C n2n C n+12n+2
×(2n)! n!n1
=(n+1)!(n+1)! (2n+2)!
=(n+1)(n+1) (2n+2)(2n+1)
．n2+2n+1 4n2+6n+2
∴lim n→∞
=C n2n C n+12n+2 lim n→∞
=n2+2n+1 4n2+6n+2
．1 4
故选D．