英语语法中，主动语态和被动语态是两种常用的语态形式。在写作和口语表达中，我们需要灵活运用这两种语态，以便更加准确地表达自己的意思。下面是20个常用的主动句变被动句的例子：
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主动句：She wrote the letter. 被动句：The letter was written by her.
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主动句：He is cooking dinner. 被动句：Dinner is being cooked by him.
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主动句：They have finished the project. 被动句：The project has been finished by them.
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主动句：He will teach the class. 被动句：The class will be taught by him.
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主动句：She gave me the book. 被动句：The book was given to me by her.
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主动句：He can fix the car. 被动句：The car can be fixed by him.
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主动句：They should clean the house. 被动句：The house should be cleaned by them.
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主动句：She is reading a book. 被动句：A book is being read by her.
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主动句：He has bought a new car. 被动句：A new car has been bought by him.
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主动句：They are painting the walls. 被动句：The walls are being painted by them.
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主动句：She will cook dinner. 被动句：Dinner will be cooked by her.
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主动句：He gave her a gift. 被动句：A gift was given to her by him.
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主动句：They can fix the problem. 被动句：The problem can be fixed by them.
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主动句：She should finish the report. 被动句：The report should be finished by her.
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主动句：He is driving the car. 被动句：The car is being driven by him.
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主动句：They have booked a hotel. 被动句：A hotel has been booked by them.
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主动句：She will sing a song. 被动句：A song will be sung by her.
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主动句：He gave the keys to her. 被动句：The keys were given to her by him.
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主动句：They are building a house. 被动句：A house is being built by them.
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主动句：She can speak French. 被动句：French can be spoken by her.
以上20个例子是主动句变被动句的常用形式，我们可以根据具体情况进行灵活运用。掌握这些语法知识，可以让我们的英语表达更加准确和流畅。
