How to remove Form element from List?

Question

C++ / C#

There is this code:

public class Randoms
    {
        public static Random rnd = new Random();
        public void GoNext()
        {
            List<Form> LF = new List<Form>();
            LF.Add(new Form1());
            LF.Add(new Form2());
            LF.Add(new Form3());

            var index = rnd.Next(LF.Count);
            if (LF.Count == 0)
            {
                Results RS = new Results();
                RS.Show();
            }
            else
            {
                LF[index].Show();
                LF.RemoveAt(index);
            }
        }
    }

The main form has a button, like all other forms, it calls this method. The method, in turn, creates a sheet with forms, selects a random one and displays it on the screen, and as planned, it should remove it from the sheet, but the forms are still repeated. What is the problem?