牙科点焊机的工作原理是
A.熔焊B.电阻焊C.电流感应加热D.离心E.涡流
参考答案:B
解析:点焊属于电阻焊类型,是利用电流通过金属时产生的电阻热来熔焊。
锯割薄板式管子,可用()锯条。
A、粗齿
B、细齿
C、粗齿或细齿
D、任何工具
My elder brother _____ serve in the army. He is now a policeman. [ ]
A. used to being
B. used to
C. was used to
D. is used to