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
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。