hundred后加year还是years

hundred后加year还是years one and a half 后加year 还是years three hundred years 与 three-hundred-year 的区别? about后加hundreds of还是three hundred(具体数字) year olds还是years old? a girl of 后面加eight years old还是eight-year-old?为什么,麻烦详细一点 More than seven hundred years ago,a 17-year-old ltalian boy One Hundred Years 歌词 a hundred years 为什么two-year-old的year不加S而two-hundred-words的word要加S two hundred 后要不要加s啊? a few years' time中的year为何要加s'