被动语态什么时候要加by?什么时候又不用?答好给你100分!555

网友回答

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.
======以下答案可供参考======
供参考答案1:
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