求两道题的 解答，有兴趣来看看

  string s = "aa aa bb ccd";
            var list = s.Split(' ').ToList();
            foreach (var t in list.FindAll(c => c.Length == list.Max(t => t.Length)))
            {
                Console.WriteLine(t);
            }
            var groupBy = list.GroupBy(c => c);
            var max = groupBy.Max(k => k.Count());
            Console.WriteLine(groupBy.FirstOrDefault(k => k.Count() == max).Key);