using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ConsoleApplication1{    //为了便于观看，我就把接口和类都写在一个.cs文件中了    public interface ISay    {        void Say();    }    class Student : ISay    {        public void Say()        {            Console.WriteLine("我是一个学生,我的任务是学习");        }    }    class Teacher : ISay    {        public void Say()        {            Console.WriteLine("我是一个老师，我的任务是教书育人");        }    }    class Program    {        static void Main(string[] args)        {            Introduce(new Student());            Introduce(new Teacher());            Console.ReadKey();        }        public static void Introduce(ISay h)        {            h.Say();        }    }}