一般不加
如果作定语,要加,而且third后面的s去掉( ) 20. _______ of the earth _______ made up of oceans.A. Two-third; isB. Two-thirds; is C. Two-third; are D. Two-thirds; are选择什么这里只能选B为什么？你不是说加—，需要去掉后面的s吗？上面我有讲错的地方。请看下面的解释：two third和two-thirds区别two third和two-thirds区别two third是表时间:两点三分.two-thirds,表示分数:三分之二.顺便给你讲一下英语中分数的表达方法:分子用基数词,分母用序数词,当分子大于1时,分母加S,分子与分母之间可以用连字符"-",也可以不用.如三分之一就是one-third或a-third或one third或a third,而五分之二就是two-fifths或two fifths.