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
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设A和B是两个单链表，其表中元素有序递增。请分析算法的时间复杂度。其时间复杂度为(40)。
A．O(re+n-1)
B．(m+n+1)
C．O(m+n)
D．不确定
A．SQRC
B．SQDC
C．SQMC
D．SQM
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．a+b+c*d
B．(a+b)*c+d
C．(a+b)*(c+d)
D．a+b*c+d
A．ρ{R1(WY)，R2(XZ)}
B．ρ{R1(WZ),R2(XY)}
C．ρ={R1(WXY)，R2(XZ)}
D．ρ={R1(WX)，R2(YZ)}