为什么Six Years Old.中Year要加S呢?

为什么Six Years Old.中Year要加S呢? Ann's brother is only six years old中对only six years old进行提问 six-year-old boy和six years old boy 有什么区别?一样么?为什么? Mary is six years old(对six years old提问 i could swim when i was six years old为什么用swimi could swim when i was six years old为什么用swim而不是swimming When I was six years old I visited the Great Wall ,为什么when后面加过去式 请问是six-year-old还是six years old还是six-years-old?(这个空签名有个a ) six years old 和 six- year- old 和 six- year- olds的区别如题 My little brother is ____.A.a six-years old boy B.a six-year-old boy C.a six-years-old boyD.a six-year old boy l have a ------daughter.A.six years oid B.six years oid C.six-years-old D.six-years-old最好有说明啊 six years old,six-year-old,six-year-olds在用法上有什么区别?有six-years-old的形式吗? Mary,a ___ girl,is standing under the tree.A.six year old B.six years old C.six-year-oldD.six-years-old six-year-old和six years old用法有什么区别? six years old与six-year-old有什麽区别拜托了各位 05天津卷 I _______have been more than six years old when the accident happened.（为什么要填couldn't My brother is six years old.对划线部分提问 I have studied English s____ I was six years old. The boy six years old this year.哪里错了