已知数列{a n }是等差数列,S n 为其前n项和,且满足S 2 =4,S 5 =25,数列{b n }满足b n = 1 a n - a n+1 ,T n 为数列{b n }的前n项和. (1)求数列{a n }的通项公式; (2)若对任意的n∈N * ,不等式λT n <n+8?(-1) n 恒成立,求实数λ的取值范围; (3)是否存在正整数m,n(1<m<n),使得T 1 ,T m ,T n 成等比数列?若存在,求出所有m,n的值;若不存在,请说明理由.
【单选题】Which of the following is an example of how U. S. online matchmakers have adapted their business models to better serve customers from other cultures?
A.
inviting parents to fill out profiles for their children in India
B.
emphasizing the goal of finding true love in Scandinavia