造成铸造全冠就位困难的原因不包括（）
A.石膏代型磨损
B.蜡型蠕变变形
C.间隙涂料涂得过厚
D.牙颈部肩台不整齐
E.铸造冠缘过长
参考答案：C
(2013·成都一模)________ all the homework assigned by the school, the students have to work at it till midnight.
A．Completing
B．To complete
C．Having completed
D．To have completed
简述传统点火系产生高压电原理？
