C#中接口声明属性，但是提示“接口”中不能有属性。

C#中接口定义属性如下所示：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Ch08Ex05
{
    abstract  class  HotDrink
   {
      float  Milk;
      float Sugar;
     
      public int Drink(int x);
      public int AddMilk(int x);
      public int AddSugar(int x); 

   }    

     public interface ICup
  {
      int Color;
      int Volume;
      int Refill(int x);
      bool Wash();

   }
     class CupOfCoffee:HotDrink,ICup
    {
        int  BeanType;
        
        public int Drink(int x)
        {
           Console.WriteLine("Welcome,Drink a cup of Coffee??
");
          
            return x;
        }

      ... ...
}

 class CupOfTea:HotDrink,ICup
    {
        int  LeafType;
        
        public int Drink(int x)
        {
           Console.WriteLine("Welcome,Drink a cup of Tea??
");
          
            return x;
        }

      ... ...
}

    class  Program
  {
      static void Main(string[] args)
      {

         CupOfCoffee Coffee=new  CupOfCoffee();
         Coffee.Drink(2);
         ...

      }



  }


}

上面代码提示错误为：

第21行和第22行，Interfaces cannot contain fields.