只有当他长大后回首往事时,他才开始理解他父亲无私的爱.
语法的话,that是通用类
如果先行词被the only,the very,the same,the last,the best等词修饰,关系代词常用that(指人时,可以用who),例如：
This is the very book that I want to find.
That is the best film that we have seen.
I was the only person in my office that/who was invited.