Both his parents look sad ,Maybe they ___what is happened to him ,A Knew B have known
问题描述：
Both his parents look sad ,Maybe they ___what is happened to him ,A Knew B have known
答
Both his parents look sad ,Maybe they ___what has happened to him .
A Knew B have known
选项是B
【have known】是现在完成时,表示对现在造成的影响【look sad】.