铅笔and小新
合乎逻辑即可。
一般情况下，主从句时态是分别由语境决定的，并不互相牵制，互相影响。宾语从句除外。
以定语从句为例，
He married a girl whose father is a billionaire.
He married a girl whose father was a billionaire.
He married a girl whose father has been a billionnaire.
三个句子都没错，只是表意有差别。
第一个表示他娶的女孩的父亲是个亿万富翁；第二个表示女孩的父亲过去是个亿万富翁，现在是不是不知道；第三个表示女孩的父亲曾经是个百万富翁，现在已经不是了。
宾语从句涉及到主从句时态的牵制问题，因为涉及到间接引语。也就是从句的动作和主句的动作时间上有联系，所以要考虑主从句时态的搭配。
例如，宾语从句主句是过去时态，从句应该也在过去时态的范围内的时态。
He said his son was studying English.
他说他的儿子正在学英语。
主句一般过去时，从句过去进行时。
He said his son had passed CET-4.
他说他的儿子已经过了英语四级。
从句动作发生于主句动作之前。主句一般过去时，从句过去完成时。
英语学人
借鉴他人总结：
英语中六大从句用法总结1.主语从句1）主语从句可直接位于主语的位置，如果从句较长，谓语又较短，可用it作形式主语，而将从句放在句末。常见的句型有：*It is a fact\\a pity\\a question\\good news that...*It seems\\appears\\happened\\has turned out that...*It is clear\\important\\likely\\possible that...*It is said\\reported\\estimated\\has been proved that...It is said that comic books create a connection between people of the same generation.It seems that the performance is very useful.2)what引导的主语从句表示“...的东西时”，一般不用it作形式主语。What we lack is experience.3)what,who,when,why,whether等词含有各自的疑问意义，但它们引导的主语从句，都用陈述语序。How the plan is to be carried out should be discussed again.I did know why I felt like crying.2.宾语从句1）宾语从句可位于及物动词、介词和某些形容词后。连词that常可省略。介词后一般接疑问词引导的宾语从句。in that(因为),except that(除了),but that(只是）已构成固定搭配，其他介词后一般不接that引导的宾语从句。*I promised that I would change the situation.*All this is different from what American young people would say about friendship.*He is certain that watching so much television is not good for children.*This article is well-written except that it is a bit too long.2)宾语从句后如有宾补，要用形式宾语it来代替，而把宾语从句移至宾补之后。He has made it clear that he would not change his mind.3)在think,believe,suppose,expect等动词后的宾语从句中，如果谓语是否定的，一般将否定词移至主句谓语上，宾语从句则变成肯定形式。He didn't think that the money was well spent.3.表语从句表语从句出现在结构为“主语+系动词+表语从句”的句子中。表语从句除可用that,what,when,why,whether,how等引导外，还可由because,as if(though)等引导。that常可省略。如主句主语为reason,只能用that引导表语从句，不可用because.Perhaps the most important thing to remember is that there is no one common type of life in America.The reason why so many people died there is that there were not enough food supplies.It looks as if successful international cultural communication will make the world smaller.4.同位语从句同位语从句用于对前面出现的名词作进一步说明，一般用连词that引导，由于先行名词的意义不同，也可用whether,who,when,where,what,why,how等引导。常见的先行名词有fact,idea,belief,news,hope,conclusion,evidence,suggestion,order,problem,report,decision.有时由于谓语较短，将同位语从句位于谓语之后。She finally made the decision that she would join the fashion show.I had no idea how many books I could borrow at a time.The news came that their team had won the championship.5.定语从句定语从句所修饰的先行词可以是名词或代词，也可以是一个句子。定语从句通常位于先行词之后，由关系代词或关系副词引导。*限制性定语从句限制性定语从句修饰先行词，对先行词起修饰作用，紧接先行词之后，无逗号，若省去，原句意思不完整。引导定语从句的关系代词有who,whom,whose,which,that等。who,whom,whose用于指人，whose有时也可指物，相当于of which；which用于指物；that既可指人也可指物，但只用于限制性定语从句中。关系代词除了引导定语从句，替代先行词外，还在从句中担任主语、宾语、定语等。The computers and cables which make up the Internet are owned by people and organizations.Those who live alone or who are sick may have trouble in getting close to other people.The girl whose parents died in an accident is living with her grandmother.1)当先行词是all,anything,everything,something,nothing等不定代词或先行词前有first,last,any,few,much,some,no,only以及形容词最高级修饰时，只能用关系代词that引导从句。That is all that I've heard from him.He's the first person that I'm going to interview this afternoon.2)关系代词的省略在从句中作宾语的关系代词常可省略。关系代词紧跟介词，作介词宾语时不可用that，只可用which或whom引导从句，并且不可省略，但当介词位于宾语从句句末时，作为介词宾语的关系代词仍可用that，也可省略。This is one of those things with which we have to put up.This is one of those things (which\\that) we have to put up with.3)引导定语从句的关系副词有when,where,why等。关系副词在从句中作状语，意义上相当于一个“介词+which”的结构。Even in comic books where(=in which) there are no words,the stories are fully expressed through the drawings.No one knows the reason why(=for which) he was so angry that day.5.定语从句*非限制性定语从句非限制性定语从句既可修饰先行词，也可修饰整个主句，起补充说明作用，与主句之间有逗号隔开，若省去，原句意思不受影响。不可用that引导非限制性定语从句。关系词不可省略。Every object has a gravitational pull,which is rather like magnetism.*“介词+which\\whom\\whose”引导的定语从句“介词+which\\whom\\whose”可引导限制性定语从句，也可引导非限制性定语从句，该结构中介词的选择取决于从句谓语动词的固定搭配，或先行词的习惯搭配。This is the computer on which he spent all his savingsIt is written by a person with whom we are all familiar.*as引导的定语从句as引导的定语从句主要用于“such...as”及“the same...as”的结构中，代替先行词是人或物的名词。as引导非限制性定语从句时，代替整个主句，从句可位于主句之前、之后或中间。These are not such problems as can be easily solved.(as代替先行词problems)As is mentioned above,no single company or group can control what happens on the Internet.(as代替主语)6.状语从句*时间状语从句引导时间状语从句的从属连词和词组有：1）when,whenever,while,as,after,before,since,till,until,once等。We have learnt quite a lot about it since we came here.2)as soon as,hardly(scarcely)...when,no sooner...than,each(every) time,the moment,immediately(that)等。As soon as I sent an e-mail message,I received positive responses.The moment he heard the good news,he jumped with joy.*地点状语从句引导地点状语从句的连词是where,wherever.Wherever she went,she took her little daughter with her.*原因、结果和目的状语从句1）引导原因状语从句的从属连词有：because,as,since,now(that),seeing that,considering that,in that等。Considering that he is a freshman,we must say he is doing well.2)引导结果状语从句的连词有：so...that,such...that,so that,that,so等。Mickey Mouse is so attractive that the children are reluctant to leave.3)引导目的状语从句的连词有：so that,in order that,for fear that,lest等，从句常使用may,might,can,could,would等情态动词。We got up early this morning so that we could catch the first bus to the railway station.*条件和让步状语从句1）引导条件状语从句的连词和词组有if,unless,as(so) long as,on condition that,in case,provided(providing) that,supposing等。As long as you have the right equipment,you can use a telephone line to transmit computer data.2)引导让步状语从句的连词和词组有though,although,whether,even though,even if,no matter what(when,how...),whatever(whenever,wherever,however....)等。though,even if等引导状语从句可转换成含有as的部分倒装结构，具有强调意义。其结构为“形容词（副词、动词、名词）+as+主语+谓语”。No matter what you may say,I would not change my mind.Young as he is,he is quite experienced in this work.(=though he is young)Child as he is,he can speak English fluently.(=though he is a child)*方式状语从句引导方式状语从句的连词有as,just as,as if,as though等。as if,as though引导的状语从句中，谓语动词常用虚拟语气，表示与事实相反。The young man made the experiment just as the teacher had taught him.Everything went on as usual as if nothing had happened.
自然习英语
英语语法中，从句共分为六种，分别为：
- 主语从句
- 宾语从句
- 表语从句
- 同位语从句
- 定语从句
- 状语从句
以上从句的定义是由该从句在复合句中所作的成分作出的，即：作主语的句子，叫主语从句; 作宾语的句子，叫宾语从句，其他类同，不一一列出。
如：Whether he will come is not known.(主语从句)
We don't know whether he will come. (宾语从句)
所有从句有几个共同点：
第一，所有从句开头都有一连接从句的连接词，或者叫引导词，它们标志着从句的开始。其中宾语从句的连接词that可省略，定语从句中引导词在从句中作宾语时可省略。第二，所有从句中除了开头的连接词外，都要用陈述语序，也就是按“主谓宾”的顺序排列词汇。
就时态方面而言：
第三，所有自然界的客观真理性句子作从句时，从句都要用一般现在时态，主句则根据实际情况而定。如，
That the earth moves around the sun is a fact.(主语从句，地球围绕太阳转，是客观事实，用一般现在时)
第四，除去讲述自然界客观事实外，各主从句中的具体时态通常根据实际情况，也就是说话人当时的具体时间状况，来确定。举例说明：
如果大家对于“根据实际情况确定时态”有困难，那么，我再用另一种思路讲：把所有读到的句子假设成“你”“现在”要说的话，①说出此话时，已经发生的动作就是过去，用一般过去时; 如果有两个动作已经发生，那么先发生的那个动作，就是“过去的过去”，用过去完成时，后发生的用一般过去时; 如果这两个动作同时发生，那么可以都用一般过去，也可以主句用一般过去，从句用过去进行时。②说出此话时，还未发生，将要发生的动作就是将来，用一般将来时，或者强调将来某具体时刻发生，就用将来进行时。③说出此话时，正在发生的动作就是进行，用现在进行时。④强调到说话的此刻已经完成的动作，就用现在完成时。⑤表示在说话的此刻正存在的一种状态动词，就用一般现在时。主语从句：When he returned yesterday is the important question.
Where the meeting will be held tomorrow has not been decided.
宾语从句：He was asked where he had come from before and where he was living then.
It depends on whether the mayor will agree to the proposal.
表语从句：That is why I am working hard at my lessons now.
That is how I figured it. 这就是我(过去）对它的看法。
同位语从句：Yu must live with the fact that you were beat in the match.
定语从句：He gave the best speech that I had ever listened to.
This is the best speech that I have ever listened to.
状语从句：Because he was ill yesterday, he didn't go to school.
As soon as I received your letter, I come here at once.
第五，各从句中对时态的特殊要求。
① 有些从句受虚拟语气的影响，句子谓语要用should +动词原形或者其他形式。
主语从句中用虚拟语气的句型：
It be +名词/形容词+主语从句 (should+动原)
It is necessary /important /a duty that we should help the old.
② 与表示建议，要求，命令意义的词汇相关的宾语，表语，同位语从句，要用到虚拟语气，从句谓语用should +动原形式。
His suggestion is that the factory should promote their product.
③ wish ,would rather 后面的宾语从句，要用虚拟语气，所以从句谓语动词时态要考虑虚拟语气用法。
I wish/would rather I had reviewed the lesson before the text.
④ 在if 引导的条件状语从句中，当说话人表达非真实的语义时，主从句要考虑虚拟语气的用法。
⑤在有表示时间，条件意义的的状语从句时，当说话人讲述将要发生的事情，从句要用一般现在时态，主句用将来时态，这就是俗称的“主将从现”。
If it rains tomorrow, I will go to plant trees.
罗敷讲中高考英语
这个感觉还是按语意来较好。
1. 他昨天说她下午到这里。
(中文有歧义的句子)
2. 他昨天说她昨天下午到这里。
(中文意思明确)
3. 他昨天说她今天下午到这里。
(中文意思明确)
1a. He said she would come here in the afternoon. 意思比较明确, 但不全等于中文
1b. Yesterday afternoon, he said she would come here. 意思比较明确，但不全等于中文
1c Yesterday, he said she would come here in the afternoon. 意思明确
2. He said yesterday she would come here in the afternoon. 意思明确, 同1c.
3a. He said yesterday she would come here in the afternoon. 意思不明确，与2搞不清
3b. He said yesterday she will come here this afternoon. 意思明确，与中文相等
3c. He said yesterday she would come here this afternoon. 时态一致原则。3b中的she还没到，3c中的she可能到了，也可能没到。3c 这句应该还有其它的意思。
时态这种玩意，脱离了语境就比较难办。
家居三所
一般是一致原则，i think he is a good boy.
特殊的例如if引导的从句主将从现
you will be late if you get up late.
含有完成时的句子具体而定
he thought he had already finished .but he didn't.
再学习时候多记多积累就行了
