-- Which floor does John live on? He lives on the floor of the building.A. fiveB. fifth

问题补充：

-- Which floor does John live on?

-- He lives on the floor of the building.

A. five

B. fifth

C. fifteen

D. fifty

答案：

A. five

(答案→)B. fifth

C. fifteen

D. fifty

解析：根据句子意思可知本题所需要的单词为序数词，故选B