System Collections Generic C# by API

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Text;
public class MainClass
{
    public static void Main()
    {
        LinkedList list = new LinkedList();
        list.AddFirst(10);             
        list.AddLast(15);              
        list.AddLast(3);               
        list.AddLast(99);              
        list.AddBefore(list.Last, 25); 
        LinkedListNode node = list.First;
        while (node != null)
        {
            Console.WriteLine(node.Value);
            node = node.Next;
        }
    }
}