单选题

现定义如下三个类， Public class A{ Priva...

Question

现定义如下三个类，

public class A{
    Private static A a = new A()
    Private A(){}
    Public static A getA(){
        return a
    }
}
public class B{
    private static B b = null
    private B(){}
    public static B getB(){
        b = new B()
        return b
    }
}
public class C{
    private static C c = null
    static{
        c = new C()
    }
    private C(){}
    public static C getC(){
        return c
    }
}

请问属于单例模式的类是？（）

A. classA和classB

B. classB和classC

C. 只有classA

D. classA 和classC