我国古代四大发明。
造纸术;印刷术;指南针;火药。
铸造全冠面预备的间隙应为()
A.0.3~0.5mm
B.0.5~1.0mm
C.1.0~1.5mm
D.1.5~2.0mm
E.2mm以上
We'd better ____ the work now. [ ]
A. do
B. to do
C. doing