当介词by用于被动语态中时
英语中及物动词有两种语态，即主动语态和被动语态。主动语态表示主语是动作的执行者被动语态表示主语是动作的承受者。被动语态由“助动词be+及物动词的过去分词”构成。助动词be有人称、时态和数的变化。
一、被动语态的用法：
1.一般现在时的被动语态构成：is / am / are + 及物动词的过去分词
Our classroom is cleaned everyday.
I am asked to study hard.
Knives are used for cutting things.
2.一般过去时的被动语态构成：was / were + 及物动词的过去分词
A new shop was built last year.
Dinosaur eggs were laid long long ago.
3.现在完成时的被动语态构成：has / have + been + 及物动词的过去分词
This book has been translated into many languages.
Many man-made satellites have been sent up into space by many countries.
4.一般将来时的被动语态构成：will+ be + 及物动词的过去分词
A new hospital will be built in our city.
Many more trees will be planted next year.
5.含有情态动词的被动语态构成：情态动词+ be + 及物动词的过去分词
Young trees must be watered often.
Your mistakes should be corrected right now.
The door may be locked inside.
Your homework can be handed in tomorrow.
6.现在进行时的被动语态构成：am / is / are + being + 及物动词的过去分词
Uncle Wang is mending my bike now.→
My bike is being repaired by Tom now.
They are planting trees over there. →
Trees are being planted over there by them.
7.不定式的被动语态：to + be + 及物动词的过去分词
There are two books to be read. →
There are twenty more trees to be planted.
二、怎样把主动语态改成被动语态?
把主动语态改为被动语态非常简单，可以遵循以下几个步骤：
1.先找出谓语动词；
2.再找出谓语动词后的宾语；
3.把宾语用作被动语态中的主语；
4.注意人称、时态和数的变化。
例：1. Bruce writes a letter every week. →A letter is written by Bruce every week.
2. Li Lei mended the broken bike this morning.→The broken bike was mended by Li Lei this morning.
3.He has written two novels so far.→Two novels have been written by him so far.
4.They will plant ten trees tomorrow.→Ten trees will be planted by them tomorrow.
5.Lucy is writing a letter now.→A letter is being written by Lucy now.
6.You must lock the door when you leave.→the door must be locked when you leave.
三、使用被动语态应注意的几个问题：
1.不及物动词无被动语态。
What will happen in 100 years.
The dinosaurs disappeared about 65 million years ago.
2.有些动词用主动形式表示被动意义。
This pen writes well.
This new book sells well.
3.感官动词或使役动词使用省略to的动词不定式，主动语态中不带to ，但变为被动语态时，须加上to 。
例：make somebody do something→somebody+ be +made to do something
see somebody do something→somebody +be +seen to do something
A girl saw my wallet drop when she passed by.→My wallet was seen to drop by a girl when she passed by.
The boss made the little boy do heavy work.→The little boy was made to do heavy work by the boss.
4.如果是接双宾语的动词改为被动语态时，直接宾语(物)作主语，那么动词后要用介词，这个介词是由与其搭配的动词决定。
He gave me a book.→A book was given to me by him.
He showed me a ticket.→A ticket was shown to me by him.
My father bought me a new bike. →A new bike was bought for me by my father.
5.一些动词短语用于被动语态时，动词短语应当看作一个整体，而不能丢掉其中的介词或副词。
We can’t laugh him. →He can’t be laugh by us.
He listens to the radio every day. →The radio is listened to by him every day.
The nurse is taking care of the sick man. →The sick man is being taken care of by the nurse.
被动语态是 be + 过去分词的形式
如：明天你将被考核 you will be tested tomorrow.
或：明天你的教授会考核你（明天你将被你的教授考核）you will be tested by your professor tomorrow.
所以不一定后面需要有介词，如果你需要说明这项被动行为是由于某事或某人发生的，则用by将需要解释的事或人介绍出来。
没有什么其他特殊要求
by后面接的人称要用受格.
所以, by me 是对的.
例: He has been seen by me.---> 主动: I have seen him.
English will be taught by him.--->主动: He will teach English.
这样清楚了吗?
by 是介词，后面接宾语，而I 是主格嘛，所以要接宾格形式的me。
by me
用宾格
by和before再做介词时候的区别
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在表示被动时,介词不是应该用by吗?
这个要分很多情况吧，有些情况根本不需要用到by这一部分啊，一般说来，当强调动作承受者，不必说出执行者或含糊不清的执行者时，多用被动语态
被…覆盖 用英文3种
（1）be covered with （2）be covered by （3）under the coverage of be covered with与be covered by，这两个词语都有“被…覆盖”之意。介词with用于主动或被动语态均可，指“用…覆盖\/掩盖”，表状态；介词by用于被动语态，引出动作的逻辑主语，表动作。covered是cover的过去分词和过去式，作为...
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by后面加的是做这个动作的人，如果你在句中要告诉别人谁做了这个动作，那就by+sb.
英语被动句中引出动作主体的介词除了by还有哪些?
5、be made 后跟不同的介词表示不同的含义 be made of\/from 由---制成 be made in 在某地制造 be made into 被制成 Windows are made of glasses. 窗户是玻璃做的。（看不出原材料）Wine is made from grapes. 酒是葡萄酿成的。（看不出原材料）6、在be known 后常跟介词to表示“被--...
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是方式状语。分清是方式状语还是主语补语，很简单的一个方法是看此部分修饰的是哪一部分。很明显，这个句子里修饰的是动作clean,表明这个动作是由学生发出，重点并非是“屋子”由学生打扫。ps：一楼的意思是在他举得例子里，主语补足语是由现在分词来担当的，楼主莫误会，呵呵。
被动语态by后面的是什么成分
by the students是被动语态的句子中的状语成分。the students是主动语态的主句的主语成分。
蹉贞安欣： 被动语态中的＂by' 用来表示动作的执行者.by后面接的人称要用受格.所以, by me 是对的.例: He has been seen by me.---> 主动: I have seen him. English will be taught by him.--->主动: He will teach English.这样清楚了吗?
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墨玉县15915973908： 被动语态有宾语吗?被动语态中 by +主语 做什么句子成分 如 This book was written by Luxun. - ？
蹉贞安欣： 你好,让我为你提供最权威的解答吧: 首先,被动语态有时是有宾语,这时的动词就是双宾语动词,如下面的句子: He gave me a book last week.主动语态 I was given a book last week,被动语态. 在这两个句子中,都是作give 宾语. 第二个问题是.by +主语在被动语态中作方式状语,表示动作执行的方式或对象.
墨玉县15915973908： 在表示被动时,介词不是应该用by吗? - ？
蹉贞安欣： 因为这里 to 后面的不是 动作regard的执行者.如果这里要特别指出动作执行者,那需要用by,且并不是句子的to those, 它们会并存: Books are regarded by the teachers as important sources of information to the students.也就是, The teachers regard books as important sources of information to the students.
墨玉县15915973908： 被动语态by - ？
蹉贞安欣： 当没必要说出动作的执行者时就可以省略by及其后的主语,如the dog was killed,可以不加by sb. 另外省略的拼音是sheng lue 不是 yue,呵呵
墨玉县15915973908： 改为被动语态什么时候用by、for和to? - ？
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