【知识点详解】
1. 定语从句的引导词选择：在定语从句中，关系代词的选择取决于它在从句中的语法功能。例如，"This is the factory where we visited last week." 正确答案是将 "where" 替换为 "that" 或去掉 "where"，因为 "factory" 是先行词，且在从句中作宾语，可以用 "that" 或省略。
2. 介词与动词短语的连用：某些动词短语的介词不能与动词分开，如 "look for"。在 "This is the watch for which Tom is looking." 中，正确答案是将 "for" 放在 "looking" 后。
3. 宾格形式的使用：当关系代词在介词后作宾语时，应用宾格形式，如 "The person to who you spoke is a student of Grade Two." 应改为 "The person to whom you spoke is a student of Grade Two."
4. 关系代词与介词的搭配："in that" 应改为 "in which"，因为 "in" 与 "which" 搭配用于引导定语从句。
5. 非限制性定语从句的引导词：非限制性定语从句不能用 "that" 引导，所以 "The sun gives off light and warmth, that makes it possible for plants to grow." 应改为 "The sun gives off light and warmth, which makes it possible for plants to grow."
6. 全部限定词与关系代词的搭配："all the books" 这种情况下，关系代词通常用 "that"，因此 "I've read all the books which I borrowed from the library." 应改为 "I've read all the books that I borrowed from the library."
7. 序数词与关系代词的搭配："the best film" 之后的关系代词应为 "that"，故 "This is the best film which I have ever seen." 应改为 "This is the best film that I have ever seen."
8. 先行词同时指人和物：当先行词同时指人和物时，通常用 "that" 引导，如 "My father and Mr. Smith talked about things and persons who they remembered in the country." 应改为 "My father and Mr. Smith talked about things and persons that they remembered in the country."
9. everything 作为先行词时的关系代词："Everything which we saw was of great interest." 应改为 "Everything that we saw was of great interest."
10. 非限制性定语从句的关系代词："His dog, that was now very old, became ill and died." 应改为 "His dog, which was now very old, became ill and died."
11. 定语从句的原因状语表达："The reason which he didn't go to school is that he was ill." 应改为 "The reason why he didn't go to school is that he was ill."
12. 定语从句的主谓一致："Those who wants to go with me put up your hands." 应改为 "Those who want to go with me put up your hands."
13. whose 用于表示所有关系："The boy, his mother died last year, studies very hard." 应改为 "The boy, whose mother died last year, studies very hard."
14. 两个并列关系代词的使用："I have two sisters, both of them are doctors." 可以改为 "I have two sisters, both of whom are doctors."
15. 定语从句中多余的信息："We're going to visit the school where your brother works there." 应去掉 "there"，因为 "where" 已经引导了地点。
16. one of + 复数名词 + 定语从句的主谓一致："He is the only one of the students who have been invited to the English Evening." 应改为 "He is the only one of the students who has been invited to the English Evening."
17. 关系代词在句中作方式状语："That is the way which they work." 应改为 "That is the way they work." 或 "That is the way in which they work."
18. 定语从句的主语："Those have questions can ask the teachers for advice." 应改为 "Those who have questions can ask the teachers for advice."
19. 复数名词与关系代词："Who is the man who has white hairs?" 应改为 "Who are the men who have white hairs?"
20. 定语从句的时间状语："I will never forget the days which we had a good time together at the sea." 应改为 "I will never forget the days when we had a good time together at the sea."
以上知识点涉及到定语从句中关系代词的选择、介词与动词短语的连用、非限制性定语从句的引导词、主谓一致、所有关系的表达以及关系代词在从句中的各种语法功能。通过这些练习，学生可以深入理解并掌握定语从句的运用。
