using System;

public class Program

{

    public static void Main()

    {

​

    }

}

​

public class ClassA

{

}

​

public class ClassB : ClassA

{

}

​

public class ServiceA

{

    public virtual ClassA GetClass() => new ClassA();   

}

​

public class ServiceB

{

    public override ClassB GetClass() => new ClassB();  

}

​

public interface IInterfaceA

{

    public ClassA CreateClass()     

}

​

public class ImplementaceInterfaceA : IInterfaceA

{

    public ClassB CreateClass()

    {

        return null;

    }

}