public interface IFuel
    {
        Int32 Level { get; }
        void Refill();
    }
    public abstract class Vehicle
    {
        public IFuel Fuel { get; }
        public Vehicle(IFuel fuel)
        {
            Fuel = fuel;
        }

    }
    public class GasFuel : IFuel
    {

        public Int32 Level { get; private set; }
        public void Refill()
        {
            Console.WriteLine("Gas Refilled.");
            Level = 100;
        }
        public GasFuel() : base()
        {

        }
    }

    public class ElectricFuel : IFuel
    {
        public Int32 Level { get; private set; }
        public void Refill()
        {
            Console.WriteLine("Charged Battery.");
            Level = 100;
        }
    }

    //What you're proposing, which is a bit silly.
    public class ElectricCar : Vehicle
    {
        public ElectricCar():base(new ElectricFuel())
        {

        }
    }

    public class GasCar : Vehicle
    {
        public GasCar():base(new GasFuel())
        {

        }
    }