A．SELECT*FROM R WHERE E＜'2'

B．SELECT B,E FROM R WHERE E＜'2'

C．SELECT B,E FROM R HAVING E＜'2'

D．SELECT*FROM R WHERE'5'＜B

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

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

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

某系统总线的一个总线周期包含4个时钟周期，每个总线周期中可以传送64位数据。若总线的时钟频率为44MHZ，则总线带宽为(43)。

A．132MB/s

B．88MB/s

C．44MB/s

D．396MB/s