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 （1）. Third parties can introduce risk in a variety of ways from connecting with an infected laptop to unauthorized access of network resources to（2）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（4）of service attacks or steal （5） information by snooping the network. As they access the corporate network, mobile and remote users inadvertently can infect the network with （6）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.

3（）

A．renounce

B．virtUOUS

C．denlal

D．traverse

以下关于不同叶片形式离心通风机的性能描述正确的是( )。

A．在同样流量下，前向式的风压最低
B．前向式风机的效率比后向式风机低
C．前向式风机的尺寸比后向式风机大
D．后向式风机常用于输送含尘气体