——主句一般时，从句时态往前看；主句过去时，从句时态全部往前移；从句表示未来，主句从句都可跟；从句说真实事，用一般现在时；从句说与现在相反，用一般过去时；从句说与过去相反，用过去完成时；从句说将来现在，用现在完成时；从句说将来过去，用过去将来时。
[宾语从句歌诀]
宾语从句三姊妹，that，if/whether，wh-/how展风采。
展风采有三关，引导词、语序、时态在把关。
主从时态要一致，陈述语序永不变。
陈述请你选that，疑问需用if/whether连。
特殊问句作宾从，原来问词不用换。
三关过后莫得意，人称、标点需注意。
留意变脸的if/when，从句的简化记心间。
[歌诀解码]
一、三姊妹
宾语从句根据引导词的不同可分为三种类型：
1. 由that引导的宾语从句。如：
We knew (that)we should learn from each other.
2. 由if/whether引导的宾语从句。如：
Please tell me if/whether you have been to America.
3. 由who，where，how等连接代词或连接副词引导的宾语从句。如：
Can you tell me how I can get to the nearest post office?
二、三关
1. 引导词关
如果从句是陈述句，引导词用that(that在口语或非正式文体中常省略);如果从句是一般疑问句，引导词用if/whether;如果从句是特殊疑问句，引导词用由疑问词转换而来的疑问代词/副词。
2. 语序关
①陈述句变为宾语从句，语序不变，即仍用陈述语序。如：
He is an honest boy. The teacher said. →The teacher said(that)he was an honest boy.
②一般疑问句和特殊疑问句变为宾语从句，语序变为陈述语序。如：
Does he work hard?I wonder.→I wonder if/whether he works hard.
When did he leave?I don’t know. →I don’t know when he left.
3. 时态关
①如果主句是现在的时态，从句的时态可根据实际情况而定。如：
I have heard(that)he will come back next week.
②如果主句是过去的某种时态，那么从句的时态一定要用过去的某种时态。如：
He said(that)there were no classes yesterday.
注意：如果宾语从句表述的是客观真理、自然现象等时，不管主句是什么时态，从句都要用一般现在时。如：
He said that light travels much faster than sound.
三、人称的变化和标点的使用
1. 从句的主语如果是第一人称，变为宾语从句则与主句的主语一致;如果是第二人称，则与主句的宾语一致;如果是第三人称，不用变化。如：
“May I use your knife?”He asked me. →He asked me if he might use my knife.
“Do you know her telephone number?”He asked me. →He asked me if I know her telephone number.
2. 宾语从句的标点均由主句决定。主句是陈述句，用句号;主句是疑问句，用问号。如：
Who will give us a talk?I don’t know. →I don’t know who will give us a talk.
Do you know?Where does he live?→Do you know where he lives?
四、两副面孔
if和when既能引导时间状语从句，又能引导宾语从句。因此，遇到它们就要认真分析一下，它们究竟属于“两副面孔”的哪一副。如：
If it rains tomorrow，I won’t come.(时间状语从句)
I don’t know if it will rain tomorrow. (宾语从句)
五、从句的简化
1. 当主句谓语动词是find，see，watch，hear等感官动词时，从句常简化为“宾语+宾补”结构，宾补为不带to的不定式或V-ing形式。如：
She found that the wallet lay/was lying on the ground. →She found the wallet lie/lying on the ground.
2. 当主句谓语动词是hope，wish，decide，forget，plan，agree等，且主句主语与从句主语相同时，从句可简化为不定式结构。如：
She agreed that she could help me with my maths. →She agreed to help me with my maths.
3. 在连接代词/副词引导的宾语从句中，当从句主语与主句主语或间接宾语一致时，宾语从句可简化为“连接代词/副词+不定式”结构。如：
Can you tell me how I can get to the station?→Can you tell me how to get to the station
