铸造前腭杆前缘距离余留牙牙龈缘的距离（）
A.≥3mm
B.≥4mm
C.≥5mm
D.≥6mm
E.≥7mm
参考答案：D
Once fighting_____ between the two villages and many people were killed.
A．broke out
B．was broken out
C．had broken out
D．had been broken out
打乱传统的按年龄编班的做法，而按学生的能力或学习成绩编班，这是( )
A．外部分组
B．内部分组
C．设计教学法
D．道尔顿制
