linq IEnumerable Concat 方法

var empList = new Dictionary<int,List<Employee>>();
            Random r = new Random();
            int length = 10000;

            Console.WriteLine(string.Format("开始装载数据({0})...", length));
            List<Employee> _List = new List<Employee>();
            for (int i = 0; i < length; i++)
            {
                var e =new Employee()
                {
                    ID = i,
                    FName = "A" + i,
                    Age = r.Next(0, 100),
                    Sex = r.Next(0, 2) == 1 ? 'F' : 'M'
                };
                if (empList.TryGetValue(e.Age, out _List))
                    _List.Add(e);
                else
                    empList[e.Age] = new List<Employee>() { e };
            }

            IEnumerable<Employee> list = new List<Employee>();
            List<Employee> list1 = new List<Employee>();
            foreach (var item in empList)
            {
                IEnumerable<Employee> ie = item.Value.Where(p => p.Sex == 'F');
                list1.AddRange(ie);
                list.Concat(ie);
            }

            Console.WriteLine(list.ToList().Count);
            Console.WriteLine(list1.Count);

如上是我的代码，运行结果中，list.Count 为0 ，list1.Count 有值。
我想问一下这是为什么？
小弟刚接触Linq，请大神解惑 Linq IEnumerale Concat
[解决办法]
本帖最后由 q107770540 于 2013-11-27 17:51:32 编辑 list = list.Concat(ie);