8-3 有助动词肯定句子的被动语气

在上一节，我们所有的例子都只是肯定句子，句子中没有助动词，可是有些肯定句子还是有助动词的，以下是一些例子：
 
主动语气                     
现在进形式 I am writing this letter.                   
现在完程序 I have written the letter.                  
过去进形式 I was writing the letter when you came.  
过去完程序 I had written the letter before you came.  
未来式          I will write the letter.                  
未来完成式 I will have written this letter.          
未来式         I am going to see you.     
             
被动语气
 The letter is being written by me.
 The letter has been written by me.
The letter was being written by me when you came.
The letter had been written by me before you came.
The letter will be written by me.
This letter will have been written by me.
You are going to be seen by me.
 
以下是更多的例子：
 
主动语气
 I have seen him.
He is going to help you.
He will teach English.
He has helped me all my life.
He had called me before you came.
He was calling his mother when we went there.
 
被动语气
 He has been seen by me.
You are going to be helped by him.
English will be taught by him.
I have been helped by him all my life.
I had been called by him before you came.
His mother was being called by him when we went there.
 
助动词不一定和时式有关，can、should、has to等等都是助动词，这些助动词在改成被动语气的时后，都应维持原状，只需加入verb to be和过去分词即可。以下是一些例子：
 
主动语气
 I can play the piano.
I may use this room.
He must give the book to me.
You should help him.
You have to write this letter.
He ought to write this report.
 
被动语气
 The piano can be played by me.
This room may be used by me.
The book must be given to me by him.
He should be helped by you.
This letter has to be written by you.
This report ought to be written by him.