请看：every third day 每隔二天，每三天
every fourth year 每隔三年，每四年
其实，以上也可以说成：
every two days, 每隔二天，每三天
every three years每隔三年，每四年
very 序数词 单数名词真的和every 基数词 复数名词表示什么意思一样吗？应该是数字上相隔一个。再看：
He has every third day off (= he works for two days then has one day off then works for two days and so on) .
他每隔两天休息一天。
He has every two days off. 他每隔两天休息一天。
如果大家要说：每隔一个，习惯说every other
They visit us every other week.
他们隔周来看我们一次。
但是，They visit us every second week.=也是完全正确的。
再如：
I went home every other week.= I went home every second week.
我隔周回一趟家。
It has been snowing, roughly every third day, for as long as I've had the flu.
自从我得了流感以来，这段时间一直在下雪，大约每三天一场。
《柯林斯高阶英汉双解学习词典》
可以转化为：
It has been snowing, roughly every two days, for as long as I've had the flu.
自从我得了流感以来，这段时间一直在下雪，大约每三天一场。
I have a furlough every three years.
我每三年休假一次。(我认为译文：我每隔三年休假一次。)
《汉英大词典》
可以转化为：
I have a furlough every fourth year.
我每隔三年休假一次。
The quarterly magazine is a periodical published every three months.
季刊是每3个月出版一次的期刊。
《汉英大词典》
The buses go every 10 minutes.公共汽车每隔10分钟发一班车。
The patient was seen for follow-up visits once every three months
这位病人每三个月接受一次随访就诊。
《柯林斯高阶英汉双解学习词典》
There is a wish among competitors that the Federation should change the test every four years.
参赛者希望联合会每4年能对该项测试作出调整。
《柯林斯高阶英汉双解学习词典》
Take ten drops every four hours.
每隔四小时喝十滴。
《汉英大词典》
He ran in every five minutes to pump me about the case
他每隔五分钟就跑来追问我这件事。
All adult dogs are routinely wormed at least every six months.
所有的成年狗至少每半年要例行打一次虫。
My friend trims my hair every eight weeks
我朋友每8个星期为我修剪一次头发。
He said Africa was suffering badly from deforestation: for every ten trees cut down, only one was planted.
他说非洲的森林砍伐现象非常严重：每砍伐10棵树，仅种植1棵。
以上4句摘自《柯林斯高阶英汉双解学习词典》
