1. 语法一致的原则
（1）以单数名词或代词，动词不定式短语作主语时，谓语动词要用单数;主语为复数时，谓语用复数，例如：
He goes to school early every morning.
The children are playing outside.
To work hard is necessary for a student.
（2）由and或both……and连接的并列成分作主语时，谓语动词用复数。例如：
Both he and I are right.
Mr Black and Mrs Black have a son called Tom.
但并列主语如果指的是同一人，同一事物或同一概念，谓语动词用单数。例如：
His teacher and friend is a beautiful girl.
The poet and writer has come.
