网桥是一种常用的网络互联设备，它工作在OSI的(27)，在LAN中用桥接少量以太网网段时，常用的网桥是(28)。从网桥的基本原理可知网桥(29)，因此使用网桥有两个显著优点，其一是(30)，其二是利用公共通信链路实现两个远程LAN的互联。

(94)

(93)

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(91)

The　major　problem　with　E-mail　is　that　it　is(71)easy　to　use　that　people　can　become(72)with　messages(73)they　can　possibly　answer　in　a　day.　In　addition,　mail　boxes　require　some　management　to(74)messages　or　archive　those　that　might　be　required　later.　Senders　don't　always　know　about　your　E-mail　backlog　and　often　send(75)messages.

(89)

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(88)

Communication　protocols　are(66)connection-oriented　or　connectionless,(67)whether　the　sender　of　a　message　needs　to　contact　and　maintain　a　dialog　with　the　recipient　or(68)send　a　message　without　any,　prior　connect　and　with　the　hope　that　the　recipient　receives　everything.(69).These　methods(70)the　two　ways　that　communication　is　implemented　on　networks.

(86)