乳牙或恒牙早失，为维持间隙，以便后继恒牙正常萌出，常采用（）
A.倾斜移动
B.转矩
C.差动力原理
D.缺隙保持器
E.序列拔牙法
参考答案：D
— I called you yesterday evening, but there was no answer.
— Oh, sorry, perhaps I a news paper outside my bedroom.
A. read B. am reading C. was reading
D/P.T/R意指（）
A.付款交单
B.承兑交单
C.付款交单凭信托收据借单
D.承兑交单凭信托收据借单
