西欧封建制度的核心是[ ]
A．等级制
B．封君封臣制
C．特权制
D．封土制
答案：B
一个盒子里装有数量相同的红、白两种颜色的球，每个球除了颜色外都相同，摸到红球甲胜，摸到白球乙胜，如果摸球以前先将盒子里的球摇匀，则甲、乙获胜的机会（ ）．
Tony ______ go to the opera on Saturday because he is going to have a meeting. [ ]
A. can't
B. might
C. mustn't
D. should
