组成总体的各个单位必须具有某一共同的品质标志表现或数量标志值。
参考答案：对
There is a new problem involved in the popularity of private cars _______ road conditions need _______.
A．that; to be improved
B．which; to be improved
C．where; improving
D．when; improving
桩冠预备，根尖部一般应该保留填充材料的长度为（）
A.2～3mm
B.0~2mm
C.3~5mm
D.5~7mm
E.不保留
