在英语语法中，定语从句是一种非常重要的句式结构。它通常用来修饰名词或代词，使句子更加具体和生动。通过以下练习题，我们可以更好地理解和掌握定语从句的应用。

练习题一：选择合适的引导词

1. The book ________ you gave me is very interesting.

A. who B. whom C. which D. whose

2. The man ________ is standing under the tree is my uncle.

A. that B. which C. whom D. whose

3. The girl ________ hair is long is my sister.

A. who B. whom C. whose D. that

练习题二：改写句子

4. The student won the prize. His hard work made it possible.

改为：The student ________ hard work made it possible to win the prize.

5. The car broke down. It was very old.

改为：The car ________ was very old broke down.

练习题三：填空

6. This is the house ________ I lived five years ago.

7. The book ________ I borrowed from the library is very useful.

8. He is the only person ________ I can trust.

通过以上练习题，我们可以发现定语从句在实际应用中的重要性。希望这些题目能够帮助大家巩固相关知识点，并在日常学习中灵活运用。如果还有疑问，可以进一步探讨和交流。