and连接并列的两个或两个以上的人或物作主语,表示单数意义,谓语动词用单数；表示复数意义,谓语动词则用复数.
eg,1.Ham and eggs is a good breakfast.（ham and eggs 固定搭档,已成为一种食物）
2.The secretary and treasurer is abent.（the secretary and treasurer是指一个人）
3.The singer and the dancer are good friends.
2.3.句主要区别在于定冠词the的有无.