问题补充:
-Do you know the boy is sitting next to Peter?
-Yes. He is Peters friend. They are celebrating his birthday.
A. who; ninth
B. that; nineth
C. /; nineth
D. which; ninth
答案:
(答案→)A. who; ninth
B. that; nineth
C. /; nineth
D. which; ninth
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。