inheritance=yes, interfaces=no

gistfile1.cs

    abstract class Bottle
    {
        public decimal Volume { get; set; }

        public void Gulp()
        {
            Volume = Volume - 40;
        }
    }

    class CokeBottle : Bottle
    {
        public CokeBottle()
        {
            Volume = 355; // mL
        }
    }

    class WaterBottle : Bottle
    {
        public WaterBottle()
        {
            Volume = 750; // mL
        }
    }

    class Person
    {
        public void Drink(Bottle beverage)
        {
            beverage.Gulp();
        }
    }