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问题 选择题

下列关于声音的传播的说法中，正确的是

A．声音可以在真空中传播　

B．声音可以在空气中传播

C．声音速度比光速快

D．声音在各种介质中的速度一样快

答案

答案：B

声音的传播需要介质，真空不能传播声音，一般声音在固体传播最快，其次是液体，在空气中传播最慢，声速340m/s,光速3×108m/s。所以ACD错，选B。

综合

读“南昆铁路图”，完成下列问题。

（1）该铁路所连接的铁路有：A_________，B__________，C__________。

（2）写出图中地理事物的名称：D________（煤矿），E__________（铁矿），F________（水能集中分布河段）。

（3）该铁路途经地区的民族构成和经济状况如何？

（4）该铁路的建成对西南地区经济发展有何影响？
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单项选择题

To compete in today’s fast-paced competitive environment, organizations are increasingly allowing contractors, partners, visitors and guests to access their internal enterprise networks．These users may connect to the network through wired ports in conference rooms or offices, or via wireless access points．in allowing this open access for third parties, LANs become（71）. Third parties can introduce risk in a variety of ways from connecting with an infected laptop to unauthorized access of network resources to （72） activity. For many organizations,however, the operational complexity and costs to ensure safe third party network access have been prohibitive. Fifty-two percent of surveyed CISOs state that they currently use a moat and castle’s security approach, and admit that defenses inside the perimeter are weak. Threats from internal users are also increasingly a cause for security concerns．Employees with malicious intent can launch（73）of service attacks or steal （74）information by snooping the network. As they access the corporate network, mobile and remote users inadvertently can infect the network with （75） and worms acquired from unprotected public networks．Hackers masquerading as internal users can take advantage of weak internal security to gain access to confidential information.

A．venomous

B．malicious

C．felonious

D．villainous
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