有关眶底爆折正确的是：（）

A．眼部受钝器伤，眼内压骤增，使眶底骨折，眼内软组织疝入上颌窦内 

B．骨折多发生于眶下沟后部内侧 

C．可产生复视和眼球固定 

D．眶上神经分布区麻木 

E．X线拍片可见眶底下移、骨折处呈"天窗"影 

Networks can be interconnected by different devices. In the physical layer, networks can be connected by (11) or hubs, which just move the bits from one network to an identical network. One layer up we find bridges and switches, which operate at data link layer. They can accept (12) ,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 networks. If two networks have (13) network layer, the router may be able to translate between the packer formats. In the transport layer we find transport gateway, which can interface between two transport connections. Finally, in the application layer, application gateways translate message (14) . As an example, gateways between Internet e-mail and X.400 e-mail must (15) the e-mail message and change various header fields.

15（）

A.analyze

B.parse

C.delete

D.create