问题
选择题
--- Do you know the boy________ is sitting next to Peter?
--- Yes. He is Peter’s friend. They are celebrating his ________ birthday.
A．who; ninth
B．that; nineth
C．/; nineth
D．which; ninth
答案
答案：A
修饰名词boy是一个定语从句，先行词是人，所以关系词是who，九的序数词为ninth，故本题选A。