1）当there be 句型的主语是一系列事物时，谓语应与最邻近的主语保持一致。
There is a pen, a knife and several books on the desk..
There are twenty boy-students and twenty-three girl-students in the class.
2）当either or 与neither nor， 连接两个主语时，谓语动词与最邻近的主语保持一致。 如果句子是由here, there引导，而主语又不止一个时，谓语通常也和最邻近的主语一致。
Either you or she is to go.
Here is a pen, a few envelops and some paper for you.
