【导读】
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1. [单选题]functions with two layers of protocols. It can connect networks of different speeds and can be adapted to an environment as it expands.
A. The hub
B. The bridge
C. The router
D. The proxy
2. [单选题]______是Internet的核心协议。
A. X.25
B. TCP/IP
C. ICMP
D. UDP
