using System;

​

public class BaseClass {

    protected string param { get; set; }

    public BaseClass(string param) {

        this.param = param;

    }

    public virtual string getParam() {

        return this.param;  

    }

}

​

public class SomeThing {

    public SomeThing(BaseClass bc) {

        Console.WriteLine(bc.getParam());

    }

}

​

public class Child1 : BaseClass {

    public Child1(string param) : base(param) {}

    public override string getParam()  {

        return "Overrided " + base.param;   

    }

}

​

public class Child2 : BaseClass {

    public Child2(string param) : base(param) {}    

    public override string getParam()  {

        return "Second overrided " + base.param;    

    }

}

​

public class Program

{

    public static void Main()

    {

        SomeThing sth1 = new SomeThing(new BaseClass("lol"));

        SomeThing sth2 = new SomeThing(new Child1("child 1"));

        SomeThing sth3 = new SomeThing(new Child2("child 2"));

    }

}