题目

下列说法正确的是 (    )． A．直线上两点及这两点之间的部分是线段 B．线段上一点及这一点一旁的部分是射线 C．射线是直线的一半 D．两条线段相加是指把两条线段叠合在一起 答案：A【分析】 根据线段、射线、直线的概念逐项判断即可． 【详解】 A、直线上两点及这两点之间的部分是线段，此项说法正确； B、射线有端点，且向一方无限延伸，此项说法错误； C、直线、射线都是无限长的，不存在一半的说法，此项说法错误； D、两条线段相加是指把两条线段的长度相加，此项They may be just passing your office, computer bag slung (悬挂) over one shoulder. Or they may be sitting in a car outside it, causally tapping away at a laptop. They look like innocent passers-by. In fact, they are stealing your corporate secrets. Drive-by hacking is the trendy term given to the practice of breaking into wireless computer networks from outside the buildings that house them. A recent study in the UK, sponsored by RSA Data Security, found that two-thirds of organizations with wireless networks were risking their data in this way. Security experts patrolled (巡逻) several streets in the City of London seeking evidence of wireless networks in operation. Of 124 that they identified, 83 were sending data without encrypting（加密）them. Such data could readily be picked up by a passer-by armed only with a portable computer, a wireless modem and a few pieces of software that can be freely downloaded from the Internet. The data could include sensitive company documents containing valuable information. Or they could be e-mail identities and passwords that could be used by hackers to log into corporate networks as if they were legal users. Most companies using wireless networking technology do not take even the simplest of measures to protect their data. Nearly all wireless network technology comes with some basic security features that need only to be activated (激活) in order to give a minimum level of security, for example, by encrypting the data being passed over the network. Raymon Kruck, business development manager at Check Point Software, a security technology specialist, believes this could be partly a psychological problem. People see the solid walls of their building as safeguards and forget that wireless networks can extend up to 200 meters beyond physical walls. Companies without any security at all on their wireless networks make it ridiculously easy for hackers to break in. Switching on the security that comes with the network technology should be automatic. Then there are other basic steps a company can take, says Mr. Kruck, such as changing the passwords on the network from the default (默认) setting. Companies can also install firewalls, which form a barrier between the internal network and the public Internet. They should also check their computer records regularly to spot any abnormal activity, which might betray the presence of a hacker. 1.According to the study sponsored by RSA Data Security, two thirds of the subjects _______. A．had most of their company data stolen B．depended on wireless computer networks C．were exposed to drive-by hacking D．were unaware of the risk of wireless hacking 2.Whichof the following is NOT considered in the study? A．The number of computer hacking incidents. B．The number of wireless computer networks identified. C．The way in which data are sent and received. D．The way in which data are hacked and stolen. 3.Most wireless network technology has_________. A．data encryption program                 B．password security programs C．illegal-user detection                    D．firewall 4.Raymond Kruck most probably agrees that wireless network security involves ________. A．wireless signal administration              B．changes in user’s awareness C．users’ psychological health              D．stronger physical walls 5.The passage is most likely to be seen in a __________ A．book review       B．science fiction      C．textbook          D．computer magazine