a half 与half of 的区别?

a half 与half of 的区别? half与half of的区别 half a与a half的区别 a half与half a的区别 half the class 与half of the class的区别 half与half of, half of them and a half a half、the half、halves、half之间 有什么区别 in half ,at half,by half的区别和用法 half a pound of chicken 的意思 a half/half a One and a half days与 One and a half apples 有什么区别?