请问more than one student作主语时,谓语动词为什么用单数?

语法就是这么规定的：
由more than one (或more than one + 单数名词),many a + 单数名词作主语,谓语动词要用单数形式.例如：
1）More than one student has passed the examination.
2）Many a boy learns to swim before he can read.
注：如果more than后面是复数名词,则谓语动词要用复数.
more + 复名+ than one 接复数谓语.e.g.