we had a three-day vacation last week和he was the first pianist in the 70-year history of the exam
问题描述：
we had a three-day vacation last week和he was the first pianist in the 70-year history of the exam
1.为什么three-day和70-year 中间加了--
2.of the exam 的of为什么用在这个地方,为什么不是for?
答
1.three-day 是【数词+名词单数】构成的合成形容词
2.of 表所属关系