Networks can be interconnected by different devices．In the physical layer，networks can be connected by (66) 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 (67) , 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 (68) 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
(69) . As an example, gateways between Internet e-mail and X.400 e-mail must (70) the e-mail message and change various header fields.

A．analyze

B．pairs

C．delete

D．create

以下关于人力资源开发的持续性的陈述中，正确的是( )。

A．人力资源开发的持续性是指，人力资源是可以不断开发的资源
B．对人力资源的开发仅限于使用它的过程中
C．人力资源开发的机会只有一次，所以一定要把握好时机
D．人的一生所拥有的人力资源都是可以持续开发的资源