按外力矩的性质分，稳性有（）。
A．初稳性和大倾角稳性
B．初稳性和动稳性
C．静稳性和动稳性
D．横稳性和静稳性
参考答案：C
牙周病维护期应进行的内容是
A．只针对口腔卫生差的人进行宣教
B．长期服用抗生素
C．定期牙周检查及洁治
D．有问题出现时才需复查
E．复查时应每2个月拍X线片
As Millie_____ TV, Andy _____ the door. [ ]
A. was watching: was opening
B. watched; opened
C. was watching; opened
D. watched: was opening
