How do I insert a text into String?

In this example we use the String.Insert() and StringBuilder.Insert() methods to insert a text into a string.

using System;
using System.Text;

namespace Kodecsharp.Example.System
{
    public class InsertText
    {
        public static void Main(string[] args)
        {
            string text = "The fox jumps over the lazy dog";

            //
            // Insert a text into string using String.Insert() method. The method
            // accept the index where the new text will be inserted.
            //
            text = text.Insert(4, "quick brown ");
            Console.WriteLine(text);

            //
            // Insert a text into string using StringBuilder.Insert() method.
            //
            StringBuilder builder = new StringBuilder("Jackdaws love my big quartz");
            builder.Insert(21, "sphinx of ");
            Console.WriteLine(builder.ToString());

            Console.ReadLine();
        }
    }
}