when and why he came here _____not known yet .为什么填is?（is为标准答案）特殊疑问词一律按单数对待吗?或者这道题涉及就近原则?

when and why he came here _____not known yet .为什么填is?（is为标准答案）特殊疑问词一律按单数对待吗?或者这道题涉及就近原则?
when and why he came here _____not known yet .为什么填is?（is为标准答案）
特殊疑问词一律按单数对待吗?或者这道题涉及就近原则?

when and why he came here _____not known yet .为什么填is?（is为标准答案）特殊疑问词一律按单数对待吗?或者这道题涉及就近原则?
楼主,是这样的,这题是把when and why he came here 他何时,为什么来着的原因当作一件事情来看,当作一个整体,所以用is