一、被动语态用于以下几种情况
1. 不知道或没有必要指出动作的执行者。如:
Many new buildings are built in our city.
2. 强调动作的承受者。如:
The wounded man has been sent to a hospital.
3. 动作执行者有比较长的修饰语。如:
The person was supported by those who wished to have a chance to make friends with him.
4. 出于礼貌,不愿说出动作的执行者。如:
You are requested to attend the party.
二、过去分词作表语与被动语态的区别
1. 系表结构中的过去分词是表示主语的特征或状态;而被动结构则是表示主语是动作的.承受者。试比较:
Our building is surrounded with the trees.
The film is usually showed on Sunday.
2. 系表结构不能带有by引导的短语;而被动结构中可以用by引导的短语引出动作的执行者。试比较:
The book is well written.
The book was written by Lu Xun.