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状语从句是英语语法中的一种重要结构，它可以用来修饰主句，增强句子的表达效果。状语从句一般由连词引导，常见的连词有：when, while, as, since, if, unless 等等。
时间状语从句
时间状语从句一般由when, while, as等连词引导，用来表示主句中的动作发生的时间。例如：
- When I was young, I used to play basketball with my friends.
- I will call you while I am on my way to work.
- As soon as I finish my homework, I will go to bed.
原因状语从句
原因状语从句一般由because, since, as等连词引导，用来表示主句中的动作或状态的原因。例如：
- I didn't go to the party because I was tired.
- Since it's raining outside, we should stay at home.
- As he was sick, he couldn't come to the meeting.
条件状语从句
条件状语从句一般由if, unless等连词引导，用来表示主句中的动作发生的条件。例如：
- If you study hard, you will pass the exam.
- Unless you finish your work, you won't be able to go home.
- If it rains tomorrow, we will stay at home.
结论状语从句
结论状语从句一般由so, therefore, thus等连词引导，用来表示主句中的动作的结果或结论。例如：
- I am tired, so I will go to bed early tonight.
- He is a doctor, therefore he knows a lot about medicine.
- She is very busy, thus she cannot come to the party.
在使用状语从句时，需要注意主从句之间的时态、语态、语气的一致性。同时，状语从句的位置可以在主句之前或之后，但是需要注意语序的变化。
以上就是状语从句的讲解和用法，希望对大家有所帮助！
