— A single room, please. 

— OK. Will you please _____ me your ID card? 

— Sure. Here you are. [ ]

A. send

B. show

C. sell

D. serve

管内层流的平均速度是管内轴心最大速度的（）倍。

A.1.0

B.0.82

C.0.5

D.1.5