运动边界层厚度由( )参数(准则)确定。
A．ν B．Re C．ρ D．υ
参考答案：B
It was mining hard. Unfonunately we_____umbrellas with us. [ ]
A. take
B. took .
C. didn't take
D. don't take
甲乙之间有一债权债务关系，乙欠甲3万元钱到期未还，乙拒绝偿还。现甲得知丙欠乙3万元钱，也已到期，对此甲可以行使( )。
A．不安抗辩权
B．撤销权
C．同时履行抗辩权
D．代位权
