对人与自然的关系认识正确的是[ ]

A．人与自然是相互对立的

B．人是自然界的一部分

C．人能够任意主宰自然界

D．人类要先服从于自然界

Networks can be interconnected by different devices．In the physical layer，networks can be connected by (64) or Hubs, which just move the bits from one network to an identical net-work. One layer up we find bridgas and swiehes, which operate at data link layer. They can accept (65) , examine the MAC address, and forward the frames to a different network while doing minor protocol translation in the process. In the network layer, we have routers that can connect two netwoks. If two networks have (66) network layer, the router may be able to translate between the packet formats. In the transport layer we find transport gateway, which can interface between the two transport connections. Finally, in the application layer, application gateways translate message

(67) . As an example, gateways between Internet e-mail and X.400 e-mail must (68) the e-mail message and change various header fields.

66（）

A．special

B．dependent

C．similar

D．dissimilar