【Itisbesttotravelwithsomeonewhocantranslatethingsforyou.先行词是否是someone,为什么用wh来引导定语从句,怎么不用that,that用法里不有先行词是someone用that当先行词是someone时,不只用that吗?我说的是先】

　　Itisbesttotravelwithsomeonewhocantranslatethingsforyou.先行词是否是someone,为什么用wh

　　来引导定语从句,怎么不用that,that用法里不有先行词是someone用that

　　当先行词是someone时,不只用that吗?

　　我说的是先行词someone是不定代词,这里不只能用that引导吗?为什么还用who