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

不同类型热电偶的测量范围和精度都有一个量级的规定，根据经验，在允许差的等级里有Ⅰ、Ⅱ、Ⅲ的划分，其中精度最高的等级是（）

A.Ⅰ

B.Ⅱ

C.Ⅲ

D.级别一样