we will have a ______ holiday in may soon.what about going to the west lakeA.three days B.three-days C.three-days' D.three-day why?

we will have a ______ holiday in may soon.what about going to the west lakeA.three days B.three-days C.three-days' D.three-day why?
we will have a ______ holiday in may soon.what about going to the west lake
A.three days B.three-days C.three-days' D.three-day
why?

we will have a ______ holiday in may soon.what about going to the west lakeA.three days B.three-days C.three-days' D.three-day why?
D
数词与名词组成的复合形容词,用‘-’ 连接,名词不能用复数

D
三天的有两个表达方式　
three-day
three days
所以D
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D
这是“数词-名词单数” 构成的合成形容词
再如：
一个五年计划 a five-year plan
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D 属于复合形容词

D 基数词加连字符加名词的单数构成形容词。
a ten-year-old boy.