交换式局域网增加网络带宽，改善网络性能的根本原因是【 】之间的多对节点的并发连接

（8分）已知乙烯能发生以下转化关系：

试回答下列问题：

（1）写出②、④反应的化学方程式及反应类型：

②：                                                       　反应类型：          

④：                                                         反应类型：    　   

（2）乙烯和其它物质发生加成反应，不能得到的是           （填标号）。

A．CH₃CH₃

B．CH₃CHCl₂

C．CH₃CH₂OH

D．CH₃CH₂Br

患者，女性，32岁，经 * * 分娩后第2天，会阴侧切口红肿，遵医嘱给予红外线灯照射

红外线灯距伤口的距离应为（）。

A.5～10cm

B.10～20cm

C.20～30cm

D.30～50cm

E.50～70cm

两个站立点之间所标绘的各种界线、线状地物、地类名称、权属性质等调绘内容须（）、不能产生丢漏。

A.衔接

B.完整

C.连贯

D.准确

A local-area network (LAN) is a communications network that (125) a variety of devices and provides a (126) for information exchange among those devices. The scope of the LAN is small typically a single building or a cluster (丛) of buildings. The LAN is usually owned by the same organization that owns the (127) devices. The internal data rate of LAN is at least several Mb/s.

The basic of LAN communication is broadcasting. At each station, there is a transmitter/receiver that communicates over a (128) shared, By other stations. A transmission from any one station is (129) to and received by all other stations.

（126）是（）

A.broadcast

B.cable

C.control

D.interconnects

E.internet

F.meander

G.means

H.medium

I.modem

J.output switch relay

结账后，不允许再输入上一会计期间的会计凭证。( )