When and why he came here ________ yet.选什么When and why he came here ________ yetA.is not known B.are not known C.has not known D.have not known为什么选B不选D?他什么时候,为什么来的都不知道,不是过去来的,为什么不是用完成式
问题描述：
When and why he came here ________ yet.选什么
When and why he came here ________ yet
A.is not known B.are not known C.has not known D.have not known
为什么选B不选D?他什么时候,为什么来的都不知道,不是过去来的,为什么不是用完成式
答