????3.??????????
??????????????????Student??????James????????????????????????override???????д??????????????????????????????????????д????Person p = new James() { name = "James"?? studentId = 2?? Id = 4 };???????????????￡?????????????????л??????????????????SayHi??????????????SayHi?????????????????????е???????
????public  abstract class Person
????{
????public  int Id;
????public virtual void Eat()
????{
????Console.WriteLine( "?????");
????}
????public virtual void Walk()
????{
????Console.WriteLine("?????");
????}
????//??????????????????????????????Person???abstract?????????????????????????????
????public abstract void Run();
????public virtual void SayHi()
????{
????Console.WriteLine("?????????");
????}
????}
????public class Student:Person
????{
????public int studentId;
????public virtual void Eat()
????{
????Console.WriteLine("???  ?????");
????}
????public override void Walk()
????{
????Console.WriteLine("???  ?????");
????}
????public override void Run()
????{
????Console.WriteLine("???  ?????");
????}
????}
????public class James:Student
????{
????public string name;
????public override void Eat()
????{
????Console.WriteLine("James  ?????");
????}
????public override void Walk()
????{
????Console.WriteLine("James  ?????");
????}
????public override void Run()
????{
????Console.WriteLine("James  ?????");
????}
????public override  void SayHi()
????{
????Console.WriteLine("James???????");
????}
????}