留学生论文写作中最常见的就是定语从句，定语从句简言之就是从句做定语修饰前面的名词或代词，功能与形容词一样，只不过因为是句子，为了避免头重脚轻因此放在名词后面。跟前面提到的名词性从句一样，定语从句也是有自己的连接词，常见的是两类，我们称之为关系代词和关系副词。首先必须明确关系代词和关系副词的基本区别。关系代词因为是代词，功能与名词相同，在从句中所作的成分通常是主语、宾语、表语等，而关系副词在句中所作的成分只能是状语，常见的有时间状语、地点状语和原因状语。
接下来我们具体分析：
一、关系代词引导的定语从句
常见的关系代词有who, whom, whose, which, that以及as。其中who，whom指代人，which，that指代物
- who，whom引导的定语从句
- In the beginning, people whobought the tomato often got angry.
- The person(whom) you should write to is Mr. Ball.
以上两个例子都指代人，区别在于who在定语从句中既可以作主语也可以作宾语，而whom只能作宾语，且作宾语时关系词可以省略，但是对于不够熟练的同学，不建议省略。
- which, that 引导的定语从句
- They needed a plant whichdidn’t need as much water as rice.
- All the people thatcome from the country work much harder.
当指代物时，which和that可以互换，与前面指代人相同的是作宾语时，关系代词可以省略。但上述2个例子中which和that都作主语因此无法省略。
- whose 引导的定语从句
(1) I have a friend whose father is a mayor.
(2) We lived in a house whose window faces south.
whose 在定语从句中作定语，表示所属关系，使用时后面接名词作定语从句的主语、宾语或其他成分。
以上是最常见的关系代词引导的定语从句，当然，有些情况是只能使用that无法使用which的，如以下这些例句：
Is there anything that I can do for you?
This was one of the most interesting books that were sold in this book store.
That’s the only thing that we can do now.
They were talking about the persons and things that they saw in the factory.
China is not the country that it was.
I don’t like the way(that)you speak to her.
这些例句中定语从句所修饰的先行词要么是不定代词，要么含有最高级或既有人又有物或固定是the way等，这些情况只能使用that。
同时，也有只能使用which而无法使用that的情况，如：
Carol said the work would be done by October, which personally I doubt very much.
Language is the most important tool without which people can’t communicate with each other.
第一句中含有逗号隔开了主句和从句，属于非限制性定语从句，这种情况是无法使用that的。
第二句which 接在介词without后面，也就是说关系代词放在介词后时只能使用which，当然前提是指物，如若指人则只能只用whom。
二、关系副词引导的定语从句
- Do you remember one afternoon ten years ago whenI came to your house and borrowed a necklace of yours?
- I can still remember the sitting-room wheremy mother and I used to sit in the evening.
- Do you know the reason whyhe left early?
关系副词引导的定语从句比较好判断，首先区分出主句和从句，其次分析从句中的句子成分会发现一般从句是一个完整的简单句句型也就是说一般不缺主语、宾语、表语，但是缺少表示时间、地点或原因的状语，因此只需要选择相应的关系副词即可。
以上就是常见的定语从句使用的结构了，定语从句在论文中的使用一方面能够显示出作者有较高的语言运用水平，其次在表达比较复杂的句群关系时能够帮助读者理清关系，使句子逻辑清晰。
