高手帮忙回答下every four days与 every fourth day的区别

题目

高手帮忙回答下every four days与 every fourth day的区别
The Olympic Games are held ()
A.each four years
B.every fourth year
C.every four years
D.each fourth years
如果没有区别,这个又选什么呢?
不要复制别答案的给我看

答案

有区别
C.every four years
every four days每隔三天/每四天
every fourth day每一个第四天