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??\n");
 
             return x;
         }
 
       ... ...
 }
 
  class CupOfTea:HotDrink,ICup
     {
         int  LeafType;
 
         public int Drink(int x)
         {
            Console.WriteLine("Welcome,Drink a cup of Tea??\n");
 
             return x;
         }
 
       ... ...
 }
 
     class  Program
   {
       static void Main(string[] args)
       {
 
          CupOfCoffee Coffee=new  CupOfCoffee();
          Coffee.Drink();
          ...
 
       }
 
   }
 
 }

上面代码提示错误为：

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