It is best to travel with someone who can translate things for you.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

It is best to travel with someone who can translate things for you.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

这个句子的先行词就是someone啊,who是关系代词.
这里的someone是指代的人,所以用who,如果是指代的物,就可以用that了

someone是指人，可用who引导，不只用that

两者均可