构造速度是指车辆在设计时，允许车辆运行的最大速度。。
参考答案：对
为避免损伤牙龈组织，上颌前牙区舌侧基托边缘应远离龈缘（）
A.1～2mm
B.2～3mm
C.3～4mm
D.4～6mm
E.6～8mm
There isn't _____ in this lesson. [ ]
A. something difficult
B. difficult something
C. anything difficult
D. difficult anything
