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.