the six-year-olds是复数还是单数呀

the six-year-olds是复数还是单数呀 fifteen-year-olds看做单数还是复数? five -year- olds像这样的泛指做主语谓语动词用单数还是复数? -----olds are on the lake A.Five-six-year B.Five-six years C six-year-old与six-year-olds的区别 five-six-year olds是什么意思与five six-year olds的区别是什么 year olds还是years old? the class 是单数还是复数 The police 是单数还是复数 The Greens是单数还是复数 the traffic police是单数还是复数 the question是复数还是单数