Detailed explanation of C# basic inheritance and polymorphism

using System;
using ;
using ;
using ;

public class Person
{

    private string _id;
    public string id
    {
        get { return _id; }
        set { _id = value; }
    }

    /// <summary>
/// Constructor
    /// </summary>
    /// <param name="id"></param>
    public Person(string id)
    {
        _id = id;
    }

    /// <summary>
/// No parameter constructor
    /// </summary>
    /// <param name="id"></param>
    /// <param name="Class"></param>
    public Person()
    {
    }

    public string GetID()
    {
        return id;
    }

}

//<access modifier>class derived class name: base class name
public class Student : Person
{
    private string _Class;

    public string Class
    {
        get { return _Class; }
        set { _Class = value; }
    }

    /// <summary>
/// No parameter constructor
    /// </summary>
    /// <param name="id"></param>
    /// <param name="Class"></param>
    public Student()
    {

    }

    public string GetClass()
    {
        return Class;
    }
}

public class NewStudent:Student
{
    /// <summary>
/// No parameter constructor
    /// </summary>
    /// <param name="id"></param>
    /// <param name="Class"></param>
    public NewStudent()
    {
    }

    private string _NID;
    public string NID;

    public string GetNID()
    {
        return NID;
    }
}