三代無線通信系統(tǒng)的無線接口從協(xié)議結構上可以劃分為（   ）三層
According to the protocol structure, the radio interface of the third generation mobile communication system can be divided into three layers, they are  .
A.物理層
Physical layer
B.數(shù)據(jù)鏈路層
Data link layer
C.網絡層
Network layer
D.媒體層
Media layer