更多"trts|tr∈R ts∈S tr[A]ts[B])表示的是( )。"的相关试题:
[单项选择]trts｜tr∈∧ts∈S∧tr[A]θts[B]表示的是( )。
A. 等值连接
B. 连接
C. 自然连接
D. 都不是
[单项选择]要求工期是指( )所要求的工期，用Tr表示。
A. 建设方
B. 业主方
C. 施工方
D. 任务委托方
[单项选择]设关系R和S的元数分别是r和s，则集合t|t=＜tt，ts＞tr∈Rts∈S标记的是( )。
A. R∪S
B. R-S
C. R∩S
D. R×S
[单项选择]TR
A. 相对迁移率(Rm)
B. 比移值(Rf值)
C. 分配系数
D. 容量因子
E. 保留时间
[单项选择]局域网冲突时槽的计算方法如下。假设tPHY表示工作站的物理层时延，C表示光速，S表示网段长度，tR表示中继器的时延，在局域网最大配置的情况下，冲突时槽等于（）。
A. S/0.7C+2tPHY+8tR
B. 2S/0.7C+2tPHY+8tR
C. 2S/0.7C+tPHY+8tR
D. 2S/O.7C+2tPHY+4tR
[单项选择]Tr30×6表示( )螺纹，旋向为( )螺纹，螺距为( )mm。
A. 矩形， 右， 12
B. 三角， 右， 6
C. 梯形， 左， 6
D. 梯形， 右， 6
[单项选择]采用RS—232C接口标准连接PC机和Modem，其请求发送信号(RTS)的连接方向为( )。
A. DCE→DTE
B. DCE→DCE
C. DTE→DTE
D. DTE→DCE
[单项选择]固定式数字磁带录音机的PD格式中央主区TR1～TR8的8条磁迹记录双声道数字音频信号，其底部副磁迹TR2是数字音频信号的( )。
A. 格式信号
B. 备用磁迹
C. 控制信号
D. 识别信号
[单项选择]固定式数字磁带录音机的PD格式中央主区TR1～TR8的8条磁迹记录双声道数字音频信号，其底部副磁迹( )是数字音频信号的备用磁迹。
A. TR4
B. TR3
C. TR2
D. TR1
[单项选择]What should an American with sufficient medical training do in order to become a licensed doctor
A. Pass an examination to practice medicine.
B. Have two years of internship in a hospital.
C. Take extra training in a specialty.
D. Be able to prescribe medicine both as a doctor and a dentist.
[单项选择]Which statement about American education is NOT true
A. Elementary and secondary education is free and noncompulsory.
B. There are more public elementary and secondary schools than private ones.
C. Public schools are financially supported and governed by states or communities.
D. Public and private schools refer to the way in which these institutions are funded and controlled.
[单项选择]Telecommuting—substituting the computer for the trip to the job—has been ______ a solution to all kinds of problems related to office work.
A. hailed as
B. drawn out
C. borne out
D. lodged in
[单项选择]
A Canadian researcher has discovered that sound travels (21) air more than one-half kilometer an hour slower than had been believed. The discovery has surprised many engineers and scientists who learned they had been (22) the wrong speed of sound for many years.
The speed of sound in air had been (23) to be three-hundred-thirty-one-point-two-nine meters a second. But Doctor George Wong found, (24) accident, that the speed of sound is only three-hundred-thirty-one-point-one-three meters a second. That is a difference of about sixteen centimeters a second.
Doctor Wong is a member of the National Research Council of Canada. He was studying ways to (25) exactly the sound created by microphones. One of his experiments (26) a number he could use to find the speed of sound. He was (27) to learn that the speed of sound was slower than scientists had thought.
To explain the difference, Doctor Wong spent eighteen mon
A. employ
B. employed
C. using
D. used
