侧面观时，全口义齿上颌蜡堤平面应该与下列哪条线平行（）
A.下颌下缘
B.鼻翼耳屏线
C.眶耳平面
D.鼻根耳屏线
E.以上都不对
参考答案：B
What do you know about the man [A] He was not born in Beijing. [B] His parents like Beijing better than he does. [C] Beijing is the place where his parents were born.
合金工具钢的合金元素主要作用是提高淬透性、耐磨性和（）。
