推出法中,推出仪的额定行程为()
A.50mm
B.60mm
C.80mm
D.100mm
参考答案:C
多聚甲醛用于牙髓失活时,封药时间需()。
A.24~48小时
B.二到四天
C.五到七天
D.两周
E.二十天
Tom has lived in Shanghai _____ three months ago. [ ]
A. for
B. since
C. before