我参考书上说每隔两天是every third day,每三天every three days,他俩相等,怎么回事啊,无语

我参考书上说每隔两天是every third day,每三天every three days,他俩相等,怎么回事啊,无语 是"every three day"还是"every three days"(每三天) every third day每隔2天=every three days每3天? every three days 和very third day有什么区别 every three days是每隔3天一次,还是每隔2天(每3天)一次? He went there every ____. A.three day B.third days C.three d every three day;every three days应该用哪一个? every second day、every other day、every two days都是每隔一天的意思吗? Every five days 和every fourth day都是每隔四天的意思吗? every other three days =every four days 对不? every third year与every three years的区别 every third