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my maths teacher gave the textbook to all the students except()who had already taken them
答案：A
定语从句需要先行词来引导,从句中缺少的成分是主语,先行词就是the ones,特指的是the pupils,因为当有后置定语从句修饰名词时,该名词要用特指.比如the map of China,the girl who wears a hat.
ones表示泛指
some不是名词,不能做先行词
the others指"另外的",经常与one搭配,通常用法是"one...the others",
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-------------------------------some为什么不可以？这里的代词是表示特指（而some是泛指）