题目内容
虚拟存储管理系统的基础是程序的 (25) 理论，这个理论的基本含义是指程序执行时往往会不均匀地访问主存储器单元。根据此理论，Denning提出了工作集理论。工作集是进程运行时被频繁地访问的页面集合。在进程运行时，如果它的工作集页面都在 (26) 内，能够使该进程有效地运行，否则会出现频繁的页面调儿调出现象。 （25）处填（）。
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在有一台处理机CPU和两台输入/输出设备I/O1和I/O2，且能够实现抢先式多任务并行工作的多道程序内，投入运行优先级由高到低的P1，P2，P3三个作业。它们使用设备的先后顺序和占用设备时间分别是：作业P1：I/O2(30毫秒) CPU(10毫秒) I/O1(30毫秒) CPU(10毫秒)作业P2：I/O1(20毫秒) CPU(20毫秒) I/O2(40毫秒)作业P3：CPU(30毫秒) I/O1(20毫秒)在对于其他辅助操作时间可以忽略不计的假设下，作业P1，P2，P3从投入到完成所用的时间分别是 (39) 毫秒， (40) 毫秒和 (41) 毫秒。三个作业从投入运行到全部完成，CPU的利用率约为 (42) %，：U01的利用率约为 (43) %。假定在系统中仅有这三个作业投入运行，各设备的利用率指该设备的使用时间同作业进程全部完成所占用最长时间的比率。 （42）处填（）。
由于内存大小有限，为使得一个或多个作业能在系统中运行，常需要外存来换取内存。其中以作业为单位对内外存进行交换的技术称为 (44) 技术，在作业内部对内外存进行交换的技术称为 (45) 技术。用外存换内存是以牺牲程序运行时间为代价的。为提高CPU有效利用率，避免内外存的频繁交换， (45) 技术常用某种 (46) 来选择换出内存的页面，它的基础是程序的 (47) 。据此，操作系统可根据 (48) 来改善系统的性能， (48) 是一个进程在定长的执行时间区间内涉及的页面的集合。 （45）处填（）。
请根据以下资料。回答下列问题。 某项目施工现场设有混凝土搅拌站，为了赶工期，施工单位实行“三班倒”连续进行混凝土搅拌生产。附近居民意见极大，纷纷到有关管理单位反映此事，有关部门也作出了罚款等相应的处理决定。 编制环境管理体系文件的重要意义有______。
As we enter the 21st century, a new global economy draws nations ever closer. But our growing interdependence (1) on much more than technology and trade. For we are linked intrinsically (本质地) by the physical and biological webs that (2) life on our planet—and, increasingly, by the threat of their unraveling (散开). Indeed, (3) we reach across borders and face this threat together, the next century may (4) an Earth in ecological crisis, with half of all (5) gone, and our grandchildren enduring deadly floods, drought and disease (6) by global warming.When millions across America (7) the first Earth Day 30 years ago, our focus understandably was our own backyard. Our rivers were (8) on fire, and our skylines were disappearing behind a (9) of smog. America’s remarkable environmental progress in the years (10) is powerful testament (证明) to our national will, our technological prowess (超凡技术) and our (11) in a better future. Protecting the environment is today a bedrock (基本的) American value, (12) important to us as safe neighborhoods and good schools. What’s more, three decades of experience have (13) the naysayers (反对的人) wrong. Tending to the environment has not (14) our economy. (15) , our air and water are the cleanest they have been in a generation, even as we enjoy the longest economic (16) in our nations’ history.America’s responsibility now, as we mark the first Earth Day of a new millennium (一千年), is to bring these lessons to bear against new, more (17) environmental challenges. We must look well (18) our own cities and countryside, make environment a core foreign policy (19) and provide the leadership needed to put all nations on a cleaner, more sustainable path to (20) . Reed the following text. Choose the best word(s) for each numbered blank and mark A, B, C or D.20（）
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