被动语态结构
　　Ⅰ、被动语态的形式
　　被动语态是由be (助动词)+过去分词(及物动词)构成。be随主语的人称、时态和数的不同而变化。现将被动语态的各种时态形式列表如下(以provide为例) 　　

 
 一般时态
 进行时态
 完成时态
 
现在
 am provided¹
is provided
are provided
 am being provided

is being provided
are being provided
 has been provided

have been provided
过去
 was provided
were provided
 was being provided
were being provided
 had been provided
 
将来
 shall be provided
will be provided
 
 shall have been provided
will have been provided
 
过去将来
 should be provided
would be provided
 
 should have been provided
would have been provided
 

　　黑体结构是在职称英语考试中常出现的结构。
　　注：
　　① 在美语中,will和would可用于各种人称。
　　② 被动语态的一般疑问句和否定句的构成:构成一般疑问句时,将主语后的第一个助动词提至句首; 构成否定句时,将not加在第一个助动词后。例如:
　　Natural gas has been found in this area. (肯定句)
　　Has natural gas been found in this area? (疑问句)
　　Natural gas has not been found in this area. (否定句)
　　③ 带有情态动词的被动语态的构成:由情态动词can, may, must等加助动词be,再加过去分词构成。这些情态动词没有人称和数的变化。如：
　　Such shops can be seen everywhere in the city.
　　The composition must be finished next week.

　　Ⅱ、主动句转换为被动句：
　　主动句变为被动句是通过这样转换而实现的:
　　1.把主动句的宾语转换为被动句的主语;
　　2.把主动句的谓语换成被动语态;
　　3.把主动句的主语前加by构成短语,放在被动语态的谓语之后。此by…短语根据需要而定，有时可以省略。
　　如： We use coal　　 to heat homes.
　　动作执行者(主语)　　 谓语　　 宾语(动作承受者)　　状语
　　Coal is used by us to heat homes.
　　动作承受者 谓语 动作执行者 状语
　　注：
　　① 带有介词或副词的短语动词，如call on, carry out, look after, take care of等用被动语态时,应视为不可分割的一部分,后面的介饲或副词不能丢掉,如:
　　主动句：Grandma looks after my younger brother well.
　　被动句：My younger brother is well looked after (by my grandma).
　　接下来我们一块来分析几个选自《职称英语等级考试用书》上的句子：
　　1. Cement² was seldom used in building during the Middle Ages.
　　(From Dyslexia )
　　2. Dyslexia first was recognized in Europe and the United States more than 80 years ago.
　　3 However, research has shown that dyslexia is more common in males than in females³, and it is found more often in persons who are left-handed.