为什么 a four-year-old boy中的year可以不加复数,而分数two-thirds中连字符后的third就必须有s?

four-year-old为什么year不用复数形式 a four-year-old boy可以说成a four-year old boy This is a_boy.He can't look after himself A,four-years-old.B.four-years-olds,C,four- year-old为什么 This____girl is so lovely.A.four years old B.four-years-girl C.four-year-old D.six-months-old four-year-old和four year old有什么不同 only four year old意思 关于four－year－old－－－children are too young to go to schoolA four－year－oldB four－years－oldC four years oldD four year old答案是A．为什么A是对的?为什么C不对?麻烦分析一下 although和BUTHE CAN DRAW VERY WELL（）HE IS ONLY A （）BOYA THOUGH FOUR-YEAR-OLD B BUT FOUR-YEARS-OLDC ALTHOUGH FOUR-YEARS-OLD此题最多2个答案.说出答案时要写为什么这个答案 请问:是a four years old boy?还是a four year old boy?正确要肯定的 为什么 a four-year-old boy中的year可以不加复数,而分数two-thirds中连字符后的third就必须有s? This is a ___boy.He can't look after himself.A.four-years-old B four-years-olds C,four-year-old D four year old 一直分不清有连字符和没有连字符的区别 They were children.Four and five-year-olds,为什么old加s 帮忙翻译下my four year-old boy tried to start a mosh pit during naptime. is a （）girl.答案是13-year-old为什么eight-year-old不对 Mr Wang is an man.A.28-year-old B.80-year-old 为什么 Four seasons in a year. jack is a four-old( ). a one-year-old boy为什么不是an