在英语语法中，定语从句是一种常见的句式结构，用来修饰名词或代词，使其更具体、明确。定语从句通常由关系代词（如who, whom, whose, which, that）或关系副词（如where, when, why）引导，并放在被修饰的名词或代词之后。

示例一：

The book that I bought yesterday is very interesting.

在这个句子中，“that I bought yesterday”是一个定语从句，用来修饰先行词“the book”。

示例二：

This is the park where we used to play football.

这里的“where we used to play football”是定语从句，用来修饰先行词“the park”。

示例三：

Do you know the man whose car is parked outside?

在这个例子中，“whose car is parked outside”是一个定语从句，用来修饰先行词“the man”。

示例四：

The movie which/that we watched last night was fantastic.

这里，“which/that we watched last night”是定语从句，用来修饰“the movie”。

示例五：

He is the teacher who always helps students after class.

“who always helps students after class”是定语从句，用来修饰“the teacher”。

通过以上例句可以看出，定语从句在实际应用中非常灵活且实用。掌握好定语从句的用法，不仅能提高语言表达的准确性，还能让写作和口语更加生动有趣。希望这些简单的例子能帮助大家更好地理解和运用定语从句！