信息系统是指以计算机进行信息处理为基础的( )。
A．软件系统
B．人机系统
C．应用系统
D．数据系统
参考答案：B
关系模型的完整性规则是对关系的某种约束条件，包括实体完整性、 【4】 和自定义完整性。
The center of flotation of a vessel is（）.
A.the center of volume of the immersed portion of the vessel
B.the center of gravity of the water plane
C.that point at which all the vertical downward forces of weight are considered to be concentrated
D.that point at which all the vertical upward forces of buoyancy are considered to be concentrated
