那位C#高手帮我编个程

题目如下：

定义Person类，类中包含姓名，性别，出生年月字段，定义一个talk方法（方法的功能为输出“我会说中文”），定义一个带参数的talk方法（方法的功能为输出参数传递过来的我所掌握的语言）；分别定义二个子类：一个是大学生类，大学生类中talk方法输出“我会说中文、英语、俄语”，一个是小学生类，小学生类中talk方法输出“我会说中文和英语”,分别创建以上类的实例，进行测试。

是关于C#多态性的；谢了

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


namespace Person类
{
class Person
{
protected string name, sex, date;
public void talk()
{
Console.WriteLine("我会说中文");
}
public void talk(string language)
{
Console.WriteLine("我会说" + language);
}
}


class DaStudent:Person
{
public void talk()
{
Console.WriteLine("我会说中文、英语、俄语");
}
}


class XiaoStudent:Person
{
public void talk()
{
Console.WriteLine("我会说中文和英语");
}
}


class Program
{
static void Main(string[] args)
{
Person a = new Person();
Console.WriteLine("a是Person的实例，下面是a的行为:");
a.talk();
a.talk("日语");
DaStudent b = new DaStudent();
Console.WriteLine("a是DaStudent的实例，下面是a的行为:");
b.talk();
XiaoStudent c = new XiaoStudent();
Console.WriteLine("a是XiaoStudent的实例，下面是a的行为:");
c.talk();
}
}
}

class Program { static void Main(string[] args) { Person p = new Person("张三","男","1960-09-01"); Person xiao = new Pupil("李四","男","1960-09-01"); Person da = new Academician("王五","男","1960-09-01"); p.talk("中文"); xiao.talk("中文","英文"); da.talk("中文","英文","俄语"); Console.ReadLine(); } } class Person { protected string _name; protected string _sex; protected string _birthStr; public Person() { } public Person(string name , string sex,string birth) { this._name = name; this._sex = sex; this._birthStr = birth; } public void talk(string language1) { Console.WriteLine("我叫：{0}，是个{1}孩，生日是：{2}，我会说{3}。",this._name,this._sex,this._birthStr,language1); } public virtual void talk(string language1, string language2) { } public virtual void talk(string language1, string language2, string language3) { } } //小学生 class Pupil:Person { public Pupil() { } public Pupil(string name, string sex, string birth) { base._name = name; base._sex = sex; base._birthStr = birth; } public override void talk(string language1, string language2) { Console.WriteLine("我叫：{0}，是个{1}孩，生日是：{2}，在读小学，我会说{3}和{4}。",base._name,base._sex,base._birthStr,language1,language2); } } //大学生 class Academician : Person { public Academician() { } public Academician(string name, string sex, string birth) { base._name = name; base._sex = sex; base._birthStr = birth; } public override void talk(string language1, string language2, string language3) { Console.WriteLine("我叫：{0}，是个{1}孩，生日是：{2}，在读大学，我会说{3}和{4}和{5}。", base._name, base._sex, base._birthStr, language1, language2, language3); } }

很容易啊，要自己去写的。写个学生类做父类，大学生小学生继承