gistfile1.cs

public interface IEdible
{
  void Eat();
}
public interface IOrganic
{
  void ApplyDubiousHealthBenefits(Body a);
}

public class PriceyApple : IEdible, IOrganic
{
  public void Eat()
  {
    // chomp
  }
  
  public void ApplyDubiousHealthBenefits(Body a)
  {
    // a.omega3 += 5
  }
}

public static class Market
{
  List<IEdible> sales = new List<IEdible>();
  float moneyMade;

  public static void Buy(IEdible a)
  {
    sales.Add(a);
    if (a instanceof IOrganic)
      moneyMade += 10;
    else
      moneyMade += 5;
  }
}

public static class Program
{
  public static void Main() 
  {
     PriceyApple apple = new PriceyApple();
     Market.Buy(a);
  }
}