求一英语单选we are going to have a ________ holiday on May
问题描述：
求一英语单选we are going to have a ________ holiday on May
A.three days' B.three days C.three-day D.three day
求答案+解释（主要是A和C.）
答
C.three-day 正确.
两个（或以上）词中间有连字符“-”才能作定语.
另例：
an eight-year-old girl
如果是所有格形式,则前面没有冠词,即
We are going to have three days' holiday on May.