If chained - how to delete?

I'm doing an application where I have the following scenario:

I have several rules (business classes)

where they all return the client code. They are separate classes that will look for the code trial and error, if find the client code returns it and so on.

How can I use a rule without using a bunch of IFs or threaded IFs in the class that calls the others that contains the specific business rules?

For the specific classes, I used the design pattern strategy.

EX: Main Class

  public abstract class Geral
{
    public abstract string retornaCodigo(Arquivo cliente)
    {
        var codigo = "";   // logica  

        return codigo;
    }

}

//Classe derivada 1


public class derivada1 : Geral
{
    public override string retornaCodigo(Arquivo cliente)
    {

        var codigo = "";  // logica  

        return codigo;
    }

}

//Classe derivada 2



public class derivada2 : Geral
{
    public override string retornaCodigo(Arquivo cliente)
    {

        var codigo = "";    // logica 2 

        return codigo;
    }

}

//Classe derivada 3



public class derivada3 : Geral
{
    public override string retornaCodigo(Arquivo cliente)
     {

         var codigo = "";  // logica 3 

       return codigo ;
     }

}


//Classe de Negocio 



public class Negocio
{

    public string Codigo()
    {
        var arquivo = new Arquivo();
        var derivada1 = new derivada1().retornaCodigo(arquivo);

        var derivada2 = new derivada2().retornaCodigo(arquivo);
        var derivada3 = new derivada3().retornaCodigo(arquivo);


        if (derivada1.Equals(null))
        {
            return derivada1;
        }
        if (derivada2.Equals(null))
        {
            return derivada2;
        }

        if (derivada3.Equals(null))
        {
            return derivada3;
        }
        return "";
    }
}

what I wanted and that I did not have to use Ifs in the Business class for validation whether or not I found the code where it can fall under any condition gave example of 3 classes plus I have more than 15 conditions and can increase, case would be many Ifs.