代代代①，副代副②；

有介要用代③，无介关副代④。

说明：①是说用关系代词代替定语从句中的代词或名词。即将两个句子合并成定语从句时，在确定先行词后（在主句中），把另一个句子（定语从句）中的代词或名词用关系代词代替，紧跟在先行词之后即可。这里当然要记住，应把被代替的代词或名词去掉。

eg: The teacher is my brother.

He is teaching.

→The teacher who (代替代词he, 故也须将he去掉)is teaching is my brother.

②与①同理。即用关系副词代替定语从句中的副词（或作状语的介词短语）。这时的关系副词也照样紧跟在先行词之后。eg:

We visited the factory.

She worked in the factory last year.

→We visited the factory, Where (代替相当于副词作状语的介词词组in the factory) she worked last year.

③和④两句是指如果定语从句中有作状语的介词短语，保留介词就要用关系代词，或用关系副词代替整个介词短语。 eg:

I still remember that day.

I joined the Party on that day.