单项选择题 Networks can be interconnected by different devices in the physical layer networks can be connected by(1)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(2)examine the MAC address and forward the frames to a different network while doing minor protocol translation in the process in me network layer, we have routers that can connect two networks, If two networks have(3)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(4). As an example, gateways between Internet e-mail and X.400 e-mail must(5)the e-mail message and change various header fields.

单项选择题 是一种最常用的结构化分析工具，它从数据传递和加工的角度，以图形的方式刻画系统内数据的运行情况。通常使用(2)作为该工具的补充说明。(1)

单项选择题 DBS的数据独立性是指(1)；DBMS的功能之一是(2)；DBA的职责之一是(3)。编写应用程序时，需要把数据库语言嵌入在(4)中；为此应在 DBMS中提供专门设计的(5)。

单项选择题 DBMS是一种（）。

单项选择题 安全管理可分为几个级别，若任何一个用户进入系统时都必须进行注册，通常将这一级安全管理称之为(192)安全管理。在进程状态转换过程中，可能会引起进程阻塞的原因是(193)。造成计算机系统出现死锁的原因是(194)。CPU不查询设备状态，当设备准备好肘，主动向CPU提出传输请求，CPU响应的信息交换方式是(195)方式。