CCBⅡ电字空气制动(EAB)系统有()种基本操作方式。
A、4
B、5
C、6
D、7
参考答案:C
恒牙中患龋最多的部位是()
A.下颌磨牙
B.上颌磨牙
C.下颌第一、二磨牙
D.上颌第一、二磨牙
E.上下颌前磨牙
As a new graduate, he doesn't know _____ it takes to start a business here. [ ]
A. how
B. what
C. when
D. which