Why (variable of type IEnumerable

Take a look at following code:

Why result1 has 2 generic arguments?

    public class Program
    {
        public static void Main(string[] args)
        {
            IEnumerable<Test> result1 = Test1();
            Console.WriteLine(result1.GetType().GetGenericArguments().Count()); // 2

            IEnumerable<Test> result2 = Test2();
            Console.WriteLine(result2.GetType().GetGenericArguments().Count()); // 1
        }

        public static IEnumerable<Test> Test1()
        {
            return new Test[] { }.Where(t => t.Id > 1).Select(t =>
            {
                t.Id++;
                return t;
            });
        }

        public static IEnumerable<Test> Test2()
        {
            return new Test[] { }.Where(t => t.Id > 1);
        }
    }

    public class Test
    {
        public virtual int Id { get; set; }
    }