题目内容
Text 1In the villages of the English countryside there are still people who remember the good old days when no one bothered to lock their doors. There simply wasn’t any crime to worry about. Amazingly, these happy times appear still to be with us in the world’s biggest community. A new study by Dan Farmer, a gifted programmer, using an automated investigative program of his own called SATAN, shows that the owners of well over half of all World Wide Web sites have set up home without fitting locks to their doors.SATAN can try out a variety of well-known hacking tricks on an Internet site without actually breaking in. Farmer has made the program publicly available, amid much criticism. A person with evil intent could use it to hunt down sites that are easy to burgle.But Farmer is very concerned about the need to alert the public to poor security and, so far, events have proved him right. SATAN has done more to alert people to the risks than cause new disorder.So is the Net becoming more secure Far from it. In the early days, when you visited a Web site your browser simply looked at the content. Now the Web is full of tiny programs that automatically download when you look at a Web page, and run on your own machine. These programs could, if their authors wished, do all kinds of nasty things to your computer.At the same time, the Net is increasingly populated with spiders, worms, agents and other types of automated beasts designed to penetrate the sites and seek out and classify information. All these make wonderful tools for antisocial people who want to invade weak sites and cause damage.But let’s look on the bright side. Given the lack of locks, the Internet is surely the world’s biggest (almost) crime-free society. Maybe that is because hackers are fundamentally honest. Or that there currently isn’t much to steal. Or because vandalism isn’t much fun unless you have a peculiar dislike for someone.Whatever the reason, let’s enjoy it while we can. But, expect it ail to change, and security to become the number one issue, when the most influential inhabitants of the Net are selling Services they want to be paid for. The author suggests in the last paragraph that （）.
查看答案
搜索结果不匹配？点我反馈
更多问题
Text 1In the villages of the English countryside there are still people who remember the good old days when no one bothered to lock their doors. There simply wasn’t any crime to worry about. Amazingly, these happy times appear still to be with us in the world’s biggest community. A new study by Dan Farmer, a gifted programmer, using an automated investigative program of his own called SATAN, shows that the owners of well over half of all World Wide Web sites have set up home without fitting locks to their doors.SATAN can try out a variety of well-known hacking tricks on an Internet site without actually breaking in. Farmer has made the program publicly available, amid much criticism. A person with evil intent could use it to hunt down sites that are easy to burgle.But Farmer is very concerned about the need to alert the public to poor security and, so far, events have proved him right. SATAN has done more to alert people to the risks than cause new disorder.So is the Net becoming more secure Far from it. In the early days, when you visited a Web site your browser simply looked at the content. Now the Web is full of tiny programs that automatically download when you look at a Web page, and run on your own machine. These programs could, if their authors wished, do all kinds of nasty things to your computer.At the same time, the Net is increasingly populated with spiders, worms, agents and other types of automated beasts designed to penetrate the sites and seek out and classify information. All these make wonderful tools for antisocial people who want to invade weak sites and cause damage.But let’s look on the bright side. Given the lack of locks, the Internet is surely the world’s biggest (almost) crime-free society. Maybe that is because hackers are fundamentally honest. Or that there currently isn’t much to steal. Or because vandalism isn’t much fun unless you have a peculiar dislike for someone.Whatever the reason, let’s enjoy it while we can. But, expect it ail to change, and security to become the number one issue, when the most influential inhabitants of the Net are selling Services they want to be paid for. Farmer’s program has been criticized by the public because （）.
Text 4For about three centuries we have been doing science, trying science out, using science for the construction of what we call modern civilization. Every indispensable item of contemporary technology, from canal locks to dial telephone-to penicillin, was pieced together to form the analysis of data provided by one or another series of scientific experiments. Three hundred years seems a long time for testing a new approach to human inter-living, long enough to settle back for critical appraisal of the scientific method, maybe even long enough to vote on whether to go no with it or not. There is an argument.Voices have been raised in protest since the beginning, rising in pitch and violence in the nineteenth century during the early stages of the industrial revolutions, summoning urgent crowds into the streets any day on the issue of nuclear energy. Give it back, say some of the voices, it doesn’t really work, we’ve tried it and it doesn’t work, go back three hundred years and start again on something else less chancy for the race of man.The principal discoveries in this century, taking all in all, are the glimpses of the depth of our ignorance about nature. Things that used to seem clear and rational, matters of absolute certainty—Newtonian mechanics, for example—have slipped through our fingers, and we are left with a new set of gigantic puzzles, cosmic uncertainties, ambiguities. Some of the laws of physics are amended every few years, some are canceled outright, and some undergo revised versions of legislative intent as if they were acts of Congress.Just thirty year ago we call it a biological revolution when the fantastic geometry of the DNA molecule was exposed to public view and the linear language of genetics was decoded. For a while, things seemed simple and clear, the cell was a neat little machine, a mechanical device ready for taking to pieces and reassembling, like a tiny watch. But just in the last few years it has become almost unbelievably complex, filled with strange parts whose functions are beyond today’s imagining.It is not just that there is more to do; there is everything to do. What lies ahead, or what can lie ahead if the efforts in basic research are continued, is much more than the conquest of human disease or the improvement of agricultural technology of the cultivation of nutrients in the sea. As we learn more about fundamental processes of living things in general we will learn more about ourselves. The principal discovery in this century shows man has （）.
计算题 设A是4阶非零矩阵，a1，a2，a3，a4是非齐次线性方程组Ax=b的不同的解．(Ⅰ)如果a1，a2，a3线性相关，证明a1-a2，a1-a3也线性相关；(Ⅱ)如果a1，a2，a3，a4线性无关，证明a1-a2，a1-a3，a1-a4是齐次方程组Ax=0的基础解系．
已知X服从参数为1的指数分布，Y=|X|，试求： (Ⅰ)(X，Y)的分布函数F(x，y)； (Ⅱ)关于X和关于Y的边缘分布函数Fx(x)和FY(y)； (Ⅲ)X，Y的相关系数pXY．
微信支付 
支付宝支付