Which of the following statements about object oriented databse 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 subclass includes the attributes and methods of all its subclasses.

抗代谢药物主要作用于细胞周期时相的（）

A.G₁期

B.S期

C.G₂期

D.M期

E.G₀期