It was in 1997 ______ Mary left home for China for the first time in her life.
问题描述：
It was in 1997 ______ Mary left home for China for the first time in her life.
答
定语从句 了
that
答
that
答
that,强调的是“in 1997”如果把in去掉的话就是when了
答
that
强调句
it is /was ...that/who...