— Why is your father so busy these days? — He is for my grandfather’s birthday party.A.

问题补充：

— Why is your father so busy these days?

— He is for my grandfather’s birthday party.

A. preparing; ninth

B. preparing; ninetieth

C. waiting; ninth

D. waiting; ninetieth

答案：

A. preparing; ninth

(答案→)B. preparing; ninetieth

C. waiting; ninth

D. waiting; ninetieth

解析：句意：--这些天你的父亲为什么这么忙？--他在准备祖父的90岁的生日聚会。根据问句的时间状语these days可知答语应该用现在进行时。prepare for…为某事做准备；wait for…等候某事。根据第一句父亲在忙，可知父亲应该是在做准备工作而不是静静地等候。祖夫的生日不可能是9岁生日，故排除A。故选B。