题目

-Do you know the boy________ is sitting next to Peter?-Yes. He is Peter's friend. They are celebrating his ________ birthday.A．who; ninthB．that; ninethC．/; ninethD．which; ninth 答案：A解析:who 引导定语从句，在从句中作主语，其他的词为表示人的名词或代词，表示第几个生日要用序数词。

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