half of students为啥不说a half of

half of students为啥不说a half of half of the students half students和half of the students有什么区别 Half后面可不可以连用of,如half of students half与half of, half of them and a half a half 与half of 的区别? Half of the students ____ from Beijing. half of the students 还是one-second of the students a half of an hour half a day 为何不说half day.类比half apple What is twice a half of five and a half?