按你的意思,
这些词引导一个从句,用于从句开头,属于从句的句子成份(that引导名词性从句除外).
This is the bag that I talked with you the other day.(其中that引导定语从句,在从句中作宾语)
而which,who如果引导的是疑问句就要用倒装.
Who is that girl?(疑问句,be 动词位于主语that girl 之前,属倒装)
He is the man who wanted to meet you two days ago.(who 引导定语从句,在从句中作主语,后面不用倒装.)