User programs interact with the kernel through a set of standard(71). They request services to be provided by the kernel. Such services would include accessing a file: open close, read, write, link, or execute a file; starting or(72)accounting records; changing ownership of a file or(73); changing to a new directory; creating,(74), or killing a process; enabling access to hardware devices; and setting limits on system resources. Unix is a multi -user, multi -tasking operating system. You can have many users logged into a system simultaneously, each running many programs. It's the kernel's job to keep each process and user separate and to regulate access to(75), including cpu, memory, disk and other L/O devices.
A．system commands
B．system transfer
C．system calls
D．system rings
Sequential circuit is a common logic device whose output values, at a given instant, depend upon its input values and the internal state at that instant, and whose internal state depends upon the(66)preceding input values and the preceding internal state. A sequential circuit can assume a finite number of internal states and may therefore be regarded, from an abstract(67), as a finite(68).Combinational circuit is another logic device whose output values, at any given instant, depend upon the input values at that instant. A combinational circuit is a(69)of a sequential circuit whose internal state is not taken(70).
A．directly
B．immediately
C．instantly
D．snapshot
A．考虑无风险报酬率
B．高于行业基准收益率
C．低于投资机会成本
D．高于投资机会成本
以下说法错误的是(20)。
A．对象具有很强的表达能力和描述功能
B．对象是人们要进行研究的任何事务
C．对象是封装的最基本单位
D．类封装比对象封装更具体、更细致
A．基本医疗保险
B．大额医疗费用互助制度
C．企业补充医疗保险
D．医疗救助
A．系统操作员的人身安全。
B．计算机系统中的每个软件实体能安全使用，即信息不会被非法阅读、修改和泄漏。
C．操作系统本身的安全。
D．物理安全，即物理设备不被破坏以及对电磁辐射、搭线窃听等破坏行为的预防。