关于LINQ的一个问题！疑点看红色字体这行！
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Linq1
{
    public class linq2
    {
        public string firstname { get; set; }
        public string lastname { get; set; }
        public string emailaddress { get; set; }
        public override string ToString()
        {
            return string.Format("{0} {1}\nemail: {2}", firstname, lastname, emailaddress);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            List<linq2> customers=createcustomerlist();
            IEnumerable<linq2> result = from customer in customers where customer.firstname == "donna" select customer;
            Console.WriteLine("firstname==\"donna\"");
                foreach(linq2 customer in result)
                {
                Console.WriteLine(customer.ToString());
                }
                customers[3].firstname = "donna";//为什么这里赋值后，result这个变量也改了呢！是不是又自动执行了上面Ienumerable<linq2>这行；                Console.WriteLine("firstname=\"donna\"(take two)");
           
                foreach (linq2 customer in result)
                {
                    Console.WriteLine(customer.ToString());
                }
        }
        private static List<linq2> createcustomerlist()
        {
        List<linq2> customer5=new List<linq2>
        {
        new linq2{firstname="orlando",lastname="gee",emailaddress="orlando@adventure.com"},
        new linq2{firstname="donna",lastname="carreras",emailaddre