---Where does John live?---He lives on floor but he doesn’t use a lift to go up and down.

问题补充：

---Where does John live?

---He lives on floor but he doesn’t use a lift to go up and down.

A. nine

B. the ninth

C. the nineth

D. a ninth

答案：

A. nine

(答案→)B. the ninth

C. the nineth

D. a ninth

解析：考查序数词。句意：他住在第九层楼，但是他不用电梯上上下下。英语中表示在几楼用序数词表示，选项C结构有误，故选B。