定义
语态(voice) 是一种动词形式，表示主语与谓语动词所表示的动作之间的关系。
分类：
主动语态：active voice
被动语态：passive voice
构成：be+done
使用场景
1. 无需指出动作的执行者或动作执行者不明确时。
Printing was introduced into Europe from China.
2. 为强调动作的承受者。
Four people were killed and thirty-one were injured in the bomb attack.
3. 习惯说法
He was born in 1982.
4. 为了句式结构整齐修辞的需要。
Yesterday he visited our university and was welcomed by the president.
5. 文体的需要。
形式
1一般现在时
The content of each word is collected, along with the word itself.
2 现在进行时
A bridge is being built there.
3 一般过去时
He was hit by a car and his arm was broken.
4 过去进行时
He was being treated in the emergency room when I arrived at the hospital.