OSI is a theoretical model that shows how any two different systems can communicate with each other．Router, as a networking device, operate at the (71) layer of the OSI model．

A．transport

B．application

C．network

D．physical

最早对汉字的结构方式进行系统研究的人是__________，他在所著《_________________》一书中首次全面阐述了关于汉字结构的理论体系六书。