【C10】A．happilyB．occasionallyC．reluctantlyD．accurately

有一变径管流，小管直径d1，大管直径d2=2d1，则两断面雷诺数的关系是：（)A、Re1=0.5Re2B、Re1=Re2C

在完全粗糙状态下，阻力系数与（)有关。A、相对粗糙度B、Re数C、Re数和相对粗糙度D、粗糙度和Re数

层流流动的Re数满足（)。A、Re2000B、Re5000C、2000Re10000D、Re20000

I catch a cold now and then.A.alwaysB.occasionallyC.constantlyD.regularly

【C10】A．isB．areC．hadD．／

【C5】A．happilyB．occasionallyC．reluctantlyD．accurately