已知数列｛an}前n项和Sn＝kn2 若对所有n属于n* 都有an+1-an>2 则实数k的 取值范围是 A k>0 B k1 D k

a(1)=s(1)=k,a(n+1)=s(n+1)-s(n)=k(2n+1)=2nk + k,a(n) = 2(n-1)k + k,0 < a(n+1) - a(n) = 2nk + k - [2(n-1)k + k] = 2k,k > 0.