介词at, in, on的区别: 1. 表示时间，注意以下用法： (1) 表示时间的某一点、某一时刻或年龄等用 at。如： I get up at six in the morning. 我早上六点钟起床。 He got married at the age of 25. 他 25 岁结婚。 (2) 泛指一般意义的上午、下午或晚上以及月或年等较长的时间，一般用 in。如： We watch TV in the evening. 我们晚上看电视。 He went to Japan in 1946. 他于 1946 去了日本。 (3) 若表示星期几或某一特定的日期，则用 on。如： He left here on the fifth of May. 他于 5 月 5 日离开这儿。
2. 表示地点、场所、位置等，注意以下用法： (1) 表示某一点位置，用 at。如： We live at No 87 Beijing Road. 我们住在北京路 87 号。 The hospital is at the end of the street. 医院在这条街的尽头。 与名词所有格连用表示地点，也用 at。如： at my sister’s 在我姐姐家 at the doctor’s 在医务室 (2) 表示空间或范围，用 in。如： What’s in the box? 这盒子里有什么? He lives in Paris with his wife. 他同他妻子住在巴黎。 但有时两者可换用。如： The meeting was held at [in] the hotel. 会议在宾馆举行。 (3) at 与 in 的另一个区别是：at 用于指较小的地方，而 in 用于指较大的地方。如： in Shanghai 在上海 at the station 在车站 但是，大与小是相对的，有时随着说话者的着眼点不同，大地方也可能用 at(比如把一个大地方看作一个点时)。如： Our plane refuelled at London. 我们的飞机在伦敦加油。 We stopped for an hour at Moscow on our way to Paris. 我们在去巴黎的途中在莫斯科停了 1 个小时。 (4) 介词 on 用于地点，主要指在某物的表面。如： What’s on the table? 桌上有什么? There’s a wallet lying on the ground. 地上有个钱包。 注：在少数搭配中，也用介词 on。如： He works on a farm. 他在农场工作。
3. 在某些搭配中，三者的区别与英国英语和美国英语有关： in the street (英) / on the street (美) 在街上 in the road (英) / on the road (美) 在路上 in the team (英) / on the team (美) 在这个队 at the weekend (英) / on the weekend (美) 在周末 at weekends (英) / on weekends (美) 在周末 4. 有时三者的差别与搭配习惯和用法有关： in bed / on the bed 在床上 in the tree (多指树外之物) / on the tree (多指树本身之物) 在树上
介词besides,but,except的用法区别： 1. 三者都可表示“除外”，但 besides 表示一种累加关系，意指“除了什么之外，还有……”； 而 except 或 but 则表示一种排除关系，意指“除了什么之外，不再有……”。如： Besides his wife，his daughter also went to see him. 除他妻子外，他女儿也去看过他(即妻子女儿都去看过他)。 Nobody went to see him except [but] his wife. 除他妻子外，没有一个人看过他(即只有他妻子去看过他)。 注：在否定句中，besides 也表示“除……之外不再有…… ”，与but, except 同义。如： No one passed the exam besides [except] Jim. 除吉姆外，没一个人通过考试。
2. 关于 but 与 except： (1) 两者都可表示“除……外不再有……”，但含义上略有差别： but侧重指意义的几乎完整性，而 except 则侧重指后面除去的部分。比较： All are here but one. 除一个人都到了。 All are here except one. 还有一个人没到。 (2) 在现代英语中，but 的介词用法十分有限，一般说来，它只能用在下列词语之后： ① no, no one, nobody, nothing, nowhere 等 ② any, anyone, anybody, anything, anywhere 等 ③ every, everyone, everybody, everything, everywhere 等 ④ all, none 等 ⑤ who, what, where 等 Everyone knows it but you. 除你之外大家都知道。 I haven’t told anybody but you. 除你之外，我没告诉任何人。 No one but he [him] showed much interest in it. 除他之外没有一个人对此有很大兴趣。 一般说来，若没有出现上述词汇，就不宜使用介词 but，否则可能造成错句。但是 except 却没有以上限制。比较： 正：The window is never opened except in summer. 除夏天外，这扇窗户从不打开。 误：The window is never opened but in summer. (3) but 一定不能用于句首，except 通常不用于句首： 除我之外每个人都累了。 正：Everyone is tired but (except) me. 正：Everyone but (except) me is tired. 误：But (Except) me, everyone is tired. 注：except for 可用于句首，表示 except 的意思： 正：Except for me, everyone is tired.
3. 关于 except 与 except for： except 主要用来谈论同类的东西，而 except for 则主要用来谈论不同类的东西，有时含有惋惜之意。如： All compositions are well written except yours. 除了你的作文外，其他的作文都写得很好。 His composition is good except for a few spelling mistakes. 他的作文写得不错，只是有几处拼写错误。 注：若用于句首，则 except for 与 except 同义(但 except 通常不用于句首)。
4. 关于 except for 与 but for： except for 主要表示排除，but for 主要表示一种虚拟条件(与虚拟语气连用)。如： Except for me, everyone passed the exam. 除了我之外，大家都通过了考试。 But for my help, she would not have passed the exam. 若不是我的帮助，她就不会通过考试。 But for the atmosphere plants would die. 如果没有大气，植物就会死亡。 5. besides 除用作介词外，还用作副词，其意为“此外”、“而且”，可用于分句句首(通常用逗号隔开)或句尾。如： I don’t want to go; besides, I’m too tired. 我不想去，而且我也太累了。 This car belongs to Smith, and he has two others besides. 这部车是史密斯的，此外他还有两部。
宾语从句的时态: 1.主句是一般现在时，从句根据实际情况使用任何时态。 例句：The headmaster hopes everything goes well. 2.主句是过去时态，从句须用过去时态的某种形式。 例句：She was sorry that she hadn’t finished her work on time. 3.当宾语从句表示的是一个客观真理或者事实时，即使主句是过去时，从句也用一般现在时态。 例句：The teacher told his class that light travels faster than sound. 4. 如果从句的动作发生在主句之前，则从句要用过去完成时态。
宾语从句的语序: A. 宾语从句必须用陈述语序。 False: He is wondering when can he finish this difficult job. Right: He is wondering when he can finish this difficult job. B. 有时候可以用it 作形式宾语，而把真正的宾语从句放在后面。 Bad: I thought that he could finish this job in just two hours impossible. Good: I thought it impossible that he could finish this job in just two hours. C. 带有宾语从句的复合句的否定形式一般是否定主句。 Bad: I think he doesn’t like the English teacher. Good: I don’t think he likes the English teacher. D. 主句一般过去时态，从句也要用过去时态。 False: He wanted to know why he is crying in the corner. Right: He wanted to know why he was crying in the corner
宾语从句的否定转移: 主句的谓语动词是think,believe,imagine,suppose,consider,espect,fancy,guess等。 并且主句的主语是第一人称而且为一般现在时，从句的否定词一般要转移到主句上来,其反义疑问句一般与宾语从句一致。 I don’t think he will come to my party.而不能说成I think he won’t come to my party. 我认为他不会来我的舞会. I don’t believe that man is killed by Jim,is he? 我认为那个人不是Jim所杀的,是不是? 如果宾语从句中有某个含有否定意义的形容词或副词,其反义疑问句要用肯定形式。 We find that he never listens to the teacher carefully,does he? 我们发现他从来不仔细听老师讲课，是不是?
宾语从句中引导词的用法比较 在复合句中作主句的宾语，引导词有： 连词：that (that 常可省略),whether, if 代词：who, whose, what ,which 副词：when ,where, how, why 等。
（一）that引导的宾语从句（在非正式场合that可以省略） 1.可跟that从句做宾语的动词有： say, think, insist, wish, hope, demand, imagine, wonder, know, suppose, see, believe, agree, admit, deny, expect, explain, order, command, feel, dream, suggest, hear, mean, notice, prefer, request, require, propose, declare, report等。 例句：The boy believes that he will travel through space to other planets. 注意事项：当主句谓语动词是 think, believe, suppose, expect 等词，而宾语从句的意思是否定时，常把否定转移至主句表示。 例句：I don’t think it is right for him to treat you like that.
2.在以下情况中that不能省略 a.当句中的动词后接多于两个由that引导的宾语从句时，第一个that可省，但后面的that不可省。 例句：He said (that) you were too young to understand the matter and that he was asked not to tell you. b.当主句的谓语动词与that宾语从句之间有插入语时，that一般不可省。 例句：Just then I noticed, for the first time, that our master was wearing his fine green coat and his black silk cap. c.当that从句是双宾语中的直接宾语时，that不可省。 例句：I can’t tell him that his mother died. d.注:许多带复合宾语的句子，that引导的宾语从句经常移到句子后部，而用it作形式宾语。 例句：I find it necessary that we should do the homework on time.
（二）由whether,if 引导的宾语从句 1.由whether(if)引导的宾语从句，实际上是一般疑问句演变而来的。意思是“是否”。宾语从句要用陈述句语序。 一般说来，在宾语从句中whether与if可以互换使用，但在特殊情况下if与whether是不能互换的。 例句：I wonder whether(if) they will come to our party.
2.只能用whether，不能用if引导的宾语从句 a.在带to的不定式前 例句：We decided whether to walk there. b.在介词的后面 例句：I’m thinking of whether we should go to see the film. c.在动词后面的宾语从句时 例句：We discussed whether we had a sports meeting next week d.直接与or not连用时 例句：I can’t say whether or not thet can come on time.
3.只能用if不能用whether引导的宾语从句 a.if引导条件状语从句，意为“如果” 例句：The students will go on a picnic if it is sunny. b.if引导否定概念的宾语从句时 例句：He asked if I didn’t come to school yesterday. c.引导状语从句even if（即使）和as if（好象）时 例句：He talks as if he has known all about it.
if,whether在宾语从句中的区别 a.if和whether在作“是否”解时,引导宾语从句常放在动词know,ask,care,wonder,find out等之后,介词后一般不用if b.少数动词,如:leave,put,discuss,doubt后的宾语从句常用whether. c. whether后可以加or not,但是if不可以. d.在不定式前只能用whether. （如：I can’t decide whether to stay. 我不能决定是否留下。） e.避免歧异时,我们常用whether而不用if.
（三）连接代词和连接副词引导的宾语从句 这样的宾语从句实际上是由特殊疑问句变化而来的，宾语从句要用陈述句语序。 用于这种结构的动词常常是：see, say, tell, ask, answer, know, decide, show, find out, imagine, suggest, doubt, wonder, discover, understand, inform, advise等。 1.英语中的连接代词有：who,whom,whose,which,what,在句中担任主语、宾语、定语或者表语。 例句：Can you tell me whom you are waiting for? 2.英语中的连接副词有：when,where,why,how，在句中担任状语的成分。 例句：None of us knows where these new parts can be bought.
简化宾语从句常用六法： 方法一： 当主句谓语动词是hope， decide， wish， choose， agree， promise等， 且宾语从句的主语与主句主语一致时，宾语从句可简化为不定式结构。 例如： Li Ming hopes he will be back very soon. →Li Ming hopes to be back very soon. We decided that we would help him. →We decided to help him.
方法二：当主句谓语动词是know， learn， remember， forget， tell等动词， 且主句主语与从句主语一致时，宾语从句可简化为“疑问词+不定式”结构。例如： She has forgotten how she can open the window. →She has forgotten how to open the window. 注：当主句谓语动词是tell， ask， show， teach等动词， 且后带双宾语，从句主语和间接宾语一致时，宾语从句可简化为“疑问词+不定式”结构。例如： Could you tell me how I can get to the station？ →Could you tell me how to get to the station？
方法三：当主句的谓语动词是order（命令），require（需要）等时， 如果主句和从句的主语不一致，宾语从句可简化为“名词（代词）+不定式”结构。例如： The headmaster ordered that we should start at once. → The headmaster ordered us to start at once.
方法四：某些动词后的宾语从句，可以用介词加动名词（短语）等其他形式简化。例如： He insisted that he should go with us. →He insisted on going with us. The poor boy doesn’t know when and where he was born. →The poor boy doesn’t know the time and the place of his birth.
方法五：某些动词后面的宾语从句可转化为“宾语+V-ing形式（作宾语补足语）”结构。例如： Liu Ping found that there was a wallet lying on the ground. → Liu Ping found a wallet lying on the ground.
方法六：动词seem后的宾语从句，也可以用不定式（短语）来简化，但句型需要进行适当的变化。例如： It seemed that the boys were going to win. →The boys seemed to win. 除上述方法外，还有一些特殊句式的转化。例如： I found that it was difficult to learn English well. →I found it difficult to learn English well. Soon we found that the ground was covered with thick snow. →Soon we found the ground covered with thick snow. They found that the box was very heavy. →They found the box very heavy
