问题补充：
There is swimming pool in front of Jhons house.
A. an 80- metres-long
B. a 80- metre-long
C. 80 metres long
D. an 80- metre – long
答案：
A. an 80- metres-long
B. a 80- metre-long
C. 80 metres long
(答案→)D. an 80- metre – long
解析：句意：约翰家的前面有一个80米长的游泳池。80- metre – long有连词符合的合成词相当于形容词，合成词中的名词不能要复数形式，80是元音音素发音，故用an.
