【单选题】以下是对关系数据库结构的描述,请选择错误描述的选项。( )
C.
表关联是通过引用完整性定义的,这是通过主码和外码(主键或外键约束条件实现的)
【单选题】— There used to be lots of fish in the lake. — Yes, but there are very __________ now.
【简答题】The sea looks very beautiful when the sun is shining on it.It can be very terrible when there is a strong wind. The sea is very big.It covers three quarters of the earth.The sea is also very deep in s...
【单选题】看下图有关轴的结构和材料的描述中,错误的是
A.
该轴是直轴,外形阶梯,内部空心结构,可同时承受转矩和弯矩
B.
前后支承的两组轴承、主轴箱和螺钉等固定并支承主轴
C.
齿轮和套筒用键固定在主轴上,实现周向固定并传递转矩
D.
轴承在工作时承受的是径向和轴向载荷,采用的滚动轴承材料是 GCr15
【简答题】完形填空 There was a very special teacher who made a far-reaching difference in my life. Fa11,1959,the first day of class at Bethesda Chevy Chase High School was about to begin, 'Who' . I asked a senior, ...
【单选题】Look over there-there's a very long, winding path _____ up to the house. [ ]
【单选题】Look over there—there’s a very long, winding path _________ to the house.
【单选题】下列关于外部设备的描述,错误的是( )
A.
键盘根据物理结构可以分为机械式键盘、电容式键盘和薄膜式键盘
B.
鼠标按照工作原理,可以分为机械鼠标、光电鼠标
C.
目前常用的显示器按使用的元器件可以分为CRT、LED和PDP显示器
D.
衡量扫描仪的技术指标主要有分辨率、扫描幅面、色彩位数和感光元件