实体建模
参考答案：是定义一些基本体素，通过基本体素的集合运算或变形操作生成复杂形体的一种建模技术。
_____, we need to improve the equipment in our factory. [ ]
A. As it is
B. As it was
C. As it were
D. As it will be
可能为龋病病原菌侵入途径的釉质结构是
A．釉质生长线
B．釉板
C．釉丛
D．釉梭
E．釉牙本质界
