单项选择题

设有教授关系如下，(其中F：性别=“男”∧职称=“教授”)
则δF(教师)为

A．3701 王小梅女教授
B．3702 李松男助教
C．3703 杨学平男教授
D．3704 李萍女助教

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单项选择题

Which of the following statements about object oriented database is NOT correct

A．Each object has a unique object identity in the system
B．Encapsulation and inheritance are two important features of object oriented database
C．A subclass can inherit the attributes and methods of all its superclasses
D．A superclass includes the attributes and methods of all its subclasses

单项选择题

I O操作过程阶段的第四阶段是

A．数据传送阶段
B．启动阶段
C．结束传送阶段
D．结束中断阶段

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