解决共有地悲剧的办法有（）
A.对羊征税把外部性内在化
B.拍卖有限量的牧羊许可证
C.土地私有化
D.以上各项都对
参考答案：D
一、二级耐火等级的民用建筑防火区，每个防火区的最大允许长度为( )。
A．250m
B．200m
C．150m
D．100m
—Let's go to buy some presents for Millie. Because tomorrow is her birthday.
—Now? It's 11 p.m. I'm afraid the shop is ______. [ ]
A. closed
B. opened
C. close
D. open
