下列哪一项不属于成人牙周炎的特征性改变
A．牙齿移位
B．牙周袋形成
C．牙龈炎症
D．牙槽骨吸收
E．牙齿松动
参考答案：A
Although I tried my best to convince them _____the importance and urgency of the operation,
the doctors were not convinced _______ it immediately. [ ]
A. with; to perform
B. of; doing
C. on; to do
D. of; to perform
直流电动机常用的制动方法有（）。
A、反馈制动
B、反接制动
C、能耗制动
D、机械制动
