half a year 和a half years.和half year哪个正确..为什么

half a year 和a half years.和half year哪个正确..为什么 half a year ago. three years and half a year half的用法是 one and a half years 还是one and a half year?half具体的用 half a year .a half year可以么? 是one year and a half还是a year and a half?为什么? once half year,twice a year one and a half 后加year 还是years one () and a half one and a half () years or year? two years and a half 还是two year and a half half a cup of milk和a half cup of milk哪个正确 1年半 用英语怎么说a year and a half?a years and a half?one and a hal