名词性从句在句中起名词作用，可作主语、宾语、表语或同位语。引导词包括that, whether, if, who, whom, whose, what, which, when, where, how, why等。

1.1 主语从句

主语从句在句中作主语，位于谓语动词之前。

1. That he passed the exam surprised everyone. (一般过去时)
2. Whether we will go camping depends on the weather. (一般将来时)
3. What you said has deeply impressed me. (现在完成时)
4. Who will be our new manager is still unknown. (一般将来时)
5. How he solved the problem remains a mystery. (一般过去时)
6. That the earth revolves around the sun is a well-known fact. (客观真理，一般现在时)

1.2 宾语从句

宾语从句在句中作动词或介词的宾语。

1. I know that you are busy. (主句现在时，从句现在时)
2. She said that she had finished her homework. (主句过去时，从句过去完成时)
3. He asked me if I could help him. (主句过去时，从句过去时)
4. We wonder whether they will come tomorrow. (主句现在时，从句将来时)
5. Can you tell me where the nearest post office is? (主句现在时，从句现在时)
6. She was thinking about what she should do next. (介词后的宾语从句)
7. My geography teacher told me that the earth moves around the sun.

（宾语从句是客观真理，用一般现在时）

1.3 表语从句

表语从句位于系动词后，对主语进行说明。

1. The fact is that he didn't tell the truth. (一般过去时)
2. My question is whether we can finish the work on time. (一般现在时)
3. The reason was that he had missed the train. (过去完成时)
4. What surprised me was how quickly they completed the project. (一般过去时)
5. One advantage of solar energy is that it is environmentally friendly. (客观事实，一般现在时)
6. His suggestion is that we should start early. (虚拟语气)

1.4 同位语从句

同位语从句对前面的名词进行解释说明，常用名词有fact, idea, news, hope, belief, thought, doubt等。

1. The news that our team had won excited us all. (过去完成时)
2. I have no idea when he will return. (将来时)
3. There is no doubt that he is qualified for the job. (现在时)
4. The fact that the earth is round is known to all. (客观真理，一般现在时)
5. Her hope that she would pass the exam came true. (过去将来时)
6. The thought that we might be late made us hurry. (过去时)

定语从句修饰名词或代词，分为限制性定语从句和非限制性定语从句。关系代词有who, whom, whose, which, that等，关系副词有when, where, why等。

2.1 限制性定语从句

限制性定语从句是句子不可缺少的部分，去掉后会影响句意。

1. The man who is standing over there is my uncle. (现在进行时)
2. The book that I borrowed from the library is very interesting. (一般过去时)
3. This is the house where I was born. (一般过去时)
4. Do you remember the day when we first met? (一般过去时)
5. The reason why he was late was that he missed the bus. (一般过去时)
6. Students who study hard will succeed. (一般现在时)

2.2 非限制性定语从句

非限制性定语从句对主句进行补充说明，去掉后不影响主句意思完整，常用逗号与主句隔开。

1. My brother, who lives in New York, is coming to visit us. (一般现在时)
2. The sun, which gives us light and heat, is actually a star. (客观事实，一般现在时)
3. Last summer, I visited Paris, where the Eiffel Tower is located. (一般现在时)
4. Shakespeare, whose plays are famous worldwide, was born in 1564. (一般现在时)
5. Mr. Smith, whom you met yesterday, is our new manager. (一般过去时)
6. The conference, which lasted three hours, was very productive. (一般过去时)

状语从句在句中作状语，可表示时间、地点、原因、条件、目的、结果、让步、比较和方式等。

3.1 时间状语从句

常用引导词：when, while, as, before, after, since, until, as soon as等。

1. When I arrived at the station, the train had already left. (主句过去完成时，从句一般过去时)
2. I will call you as soon as I get there. (主句将来时，从句一般现在时表将来)
3. While he was reading, his sister was playing the piano. (过去进行时)
4. I have lived here since I was born. (主句现在完成时，从句一般过去时)
5. Don't leave until the rain stops. (主句祈使句，从句一般现在时)
6. After he had finished his work, he went home. (主句一般过去时，从句过去完成时)

3.2 条件状语从句

常用引导词：if, unless, as/so long as, in case等。

1. If it rains tomorrow, we will stay at home. (真实条件，主句将来时，从句一般现在时)
2. You won't pass the exam unless you study hard. (真实条件，主句将来时，从句一般现在时)
3. If I were you, I would accept the offer. (虚拟现在，主句would do，从句过去式)
4. If he had taken my advice, he wouldn't have made such a mistake. (虚拟过去，主句would have done，从句had done)
5. If it should rain, the match would be postponed. (虚拟将来，主句would do，从句should do)
6. I'll lend you the money as long as you promise to return it. (真实条件，主句将来时，从句一般现在时)

3.3 原因状语从句

常用引导词：because, since, as, now that等。

1. I didn't go to the party because I was tired. (一般过去时)
2. Since everyone is here, let's begin our meeting. (一般现在时)
3. As you weren't ready, we went without you. (一般过去时)
4. She was late because she had missed the bus. (主句一般过去时，从句过去完成时)
5. Now that you have finished your work, you can go home. (现在完成时)
6. He succeeded because he worked hard. (一般过去时)

3.4 让步状语从句

常用引导词：though, although, even if, even though, no matter how/what/who等。

1. Although it was raining, we went out for a walk. (一般过去时)
2. I'll help you even if I'm very busy. (主句将来时，从句一般现在时)
3. Though he is young, he knows a lot. (一般现在时)
4. No matter how difficult the problem is, we must solve it. (一般现在时)
5. She kept working even though she was tired. (一般过去时)
6. Much as I admire his courage, I don't think he was right. (倒装让步状语从句)

3.5 目的状语从句

常用引导词：so that, in order that, lest, for fear that等。

1. He got up early so that he could catch the first bus. (主句一般过去时，从句could do)
2. I'm saving money so that I can buy a new car. (主句现在进行时，从句can do)
3. She spoke slowly in order that everyone might understand her. (主句一般过去时，从句might do)
4. We must hurry lest we should be late. (主句一般现在时，从句should do)
5. He wrote the number down for fear that he would forget it. (主句一般过去时，从句would do)
6. I'll explain it again so that you will understand it better. (主句将来时，从句will do)

3.6 结果状语从句

常用引导词：so...that, such...that, so that等。

1. He was so tired that he fell asleep immediately. (一般过去时)
2. It was such a good movie that I watched it twice. (一般过去时)
3. She spoke so fast that I couldn't understand her. (一般过去时)
4. The box is so heavy that I can't lift it. (一般现在时)
5. He worked so hard that he made himself ill. (一般过去时)
6. It was such a beautiful day that we decided to go for a picnic. (一般过去时)

3.7 比较状语从句

常用引导词：than, as...as, not so/as...as, the more...the more等。

1. He is taller than I (am). (一般现在时)
2. She works as hard as her brother (does). (一般现在时)
3. This book is not so interesting as that one (is). (一般现在时)
4. The more you practice, the better you will become. (主句一般现在时，从句将来时)
5. He ran faster than I expected. (主句一般过去时，从句一般过去时)
6. She speaks English more fluently than her teacher (does). (一般现在时)

3.8 方式状语从句

常用引导词：as, as if, as though等。

1. Do as I told you. (一般过去时)
2. He acted as if nothing had happened. (虚拟语气，过去完成时)
3. She treats me as though I were her own child. (虚拟语气，过去式)
4. It looks as if it is going to rain. (真实语气，现在进行时)
5. He talks as if he knew everything. (虚拟语气，过去式)
6. She closed her eyes as though she were tired. (虚拟语气，过去式)

从句类型	主要时态规则	注意事项
名词性从句	通常与主句时态保持一致	客观真理用一般现在时；主句过去时，从句相应过去时态
定语从句	与被修饰词的实际时间一致	不受主句时态限制
时间状语从句	主句将来时，从句现在时表将来	其他情况根据时间关系选择
条件状语从句	真实条件：主句将来时，从句现在时	虚拟条件有特殊时态要求
其他状语从句	根据实际时间关系选择	目的状语从句常用情态动词