计算机网络功能分层结构模型中存在的物理通信的层数有【】A．1 B．2 C．3 D

What ___________ he ___________ now? [ ]

A. is, do

B. is, doing

C. does, does

_____ the two designs, and you will find what problem there is with yours. [ ]

A. Comparing

B. Compared

C. To compare

D. Compare

医学道德规范

挥发油应避光、低温、密闭保存。

警犬训练员属治安警察。( )