此时国内不少书认为，这两个结构作主语，谓语均用单数。如：
One and a half months has passed. / A month and a half has passed. 已经过去了一个半月。
但是，国外一些词书则认为，谓语动词的数取决于这两个结构中名词的数：
One and a half months have passed. / A month and a half has passed. 已经过去了一个半月。
6.“the [a] number of+名词”作主语
该结构若用定冠词，其后谓语用单数；若用不定冠词，其后谓语用复数：
The number of students is 4000. 学生人数为4000。
A number of people were absent from the meeting. 许多人开会缺席。
注意类似结构：
The variety of goods in this shop is rich. 这家商店的品种丰富。
A variety of books have been published. 已出版了各种各样的书。