被動結構不一定是被，也可以是由，為，所，等等。

1. Nothing can be seen in the dark room.

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2. He appeared in the room and was warmly welcomed by the audience.

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3.       There are known to be thousands of different languages.

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4. It is reported that Taiwan authorities refused to accept any help from the mainland.

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結構補充：

It is hoped that          

It is said that            

It has been announced that  

It is assumed that          

It is considered that        

It is noticed that          

It is unanimously agreed that  

It is well-known that   

It should be realized that  

It can be said without exaggeration that