单项选择题
A． A={1,10},*为模11乘法 B． A={1,3,4,5,9},*为模11乘法 C． A为实数集合，*为普通乘法 D． A为有理数集合，*为普通加法
A． 1，2，3，4 B． 0，2，2，3 C． 1，1，2，2 D． 1，3，3，3
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 subclass includes the attributes and methods of all its subclasses.