-Do you know the boyis sitting next to Peter? -Yes,He is Peter’s friend,They are celebrati

-Do you know the boy is sitting next to Peter?
-Yes,He is Peter’s friend,They are celebrating his birthday.
A. /;nineth
B. that, nineth
C. who,ninth
D. who,the ninth

A. /;ninethB. that, nineth(答案→)C. who,ninthD. who,the ninth解析：句意：你认识那个挨着彼得的男孩吗？是的，他是彼得的朋友，他们正在庆祝他的九岁的生日。定语从句用来充当句中定语的成分，被修饰的名词叫先行词，连接主从句的是关系词。关系词分：1关系代词：who , whom , whose , which , that 。2关系副词：where,when why 等。一般的who 用于指代人的先行词，which 用来指代物的先行词，that既可指认又可指物。关系代词在从句中作主语、宾语，做宾语能省略，做主语不能省略。···岁生日，要用序数词。第九，去e加th，序数词前有修饰词，不加冠词the,故选C.

好好学习下