身披铠甲、手持盾牌和长矛的重装步兵是古希腊文明时期各城邦军队的主要组成部分（如下图），也是最受重视的部分。梭伦改革后，为雅典提供重装步兵的是

雅典重装步兵

A．第一等级

B．第二等级

C．第三等级

D．第四等级

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.

64（）

A．reapers

B．relays

C．connects

D．modems