---Will you join us to play basketball on Saturday afternoon?

---________, but I promised to go swimming with Eric.

A．Never mind

B．Many thanks

C．Take it easy

D．With pleasure

某流体在直管流动时，其雷诺数为2500，此流动属于（）。

A.层流

B.过渡流

C.湍流

D.混合流