被动语态（by+行为者）可省略
动作的行为者不分明，或不重要，或上下文中提到了行为者时，“by+行为者”可以省略。
1. The information is needed. 信息被需要。被谁需要不重要，所以省略行为者。
2. The book is being read. 书正在被读。
3. The door was opened. 门被打开了。
练习
1. The door is opened (open).(被打开了)
2. The book is being read (read).(正读着)
3. The computer has been used (use).(已经被用了)
4. The pencil has been sharpened (sharpen).(已经被削尖了)
被动语态的疑问句
（1）被动语态的一般疑问句：助动词+主语+（其他助动词）+动词过去分词~？
1. Is the information needed by him ? —>肯定句：The information is needed by him.
Yes , it is . / No , it isn’t.
2. Has the computer been used by her ? ->肯定句：The computer has been used by her.
Yes , it has . / No , it hasn’t.
3. Will the room be cleaned? ->肯定句：The room will be cleaned.
Yes , it will . / No , it won’t.
总结：肯定句的被动语态变一般疑问句通常只需把be/情态/助动词放在主语前就行。
（2）被动语态的特殊疑问句：疑问词+助动词+主语+(其他助动词)+动词过去分词~？
1. The information is needed by them. 信息被他们需要。
What is needed by him ? 对主语进行提问：什么被他们需要？
2. The girl is taken to Shanghai.. 女孩被带到上海。
Where is the girl taken ? 对地点进行提问：女孩被带到哪里？
3. The book has been read three times. 书已经被读了三遍。
How many times has the book been read ? 对次数进行提问：书已经被读了几遍？
总结：被动语态的特殊疑问句只是在被动语态的一般疑问句基础上，在句首加多了一个特殊疑问词。
练习
1. Is the book being read (read) by her ? 他正在读那本书吗？
2. Has the computer been used (use) by them ? 他们用过那台电脑吗？
3. How often is the English class taken (take)？ 英语课多长时间上一次？
来源：https://www.cnblogs.com/unlasting/p/12545448.html