在气体动力学中，当马赫数M<1时气体流动为（）；M=1时，气体的流动（）；M>1时为（）。
参考答案：亚声速流；声速流；超声速流
— Where did you pick up this wallet?
— It was in the supermarket _____ I did some shopping yesterday. [ ]
A. that
B. which
C. where
D. as
Visual FoxPro的字段有效性规则不包括( )。
A．规则
B．格式
C．信息
D．默认值
