Define an Extension Method for IEnumerable which returns IEnumerable?

Question

How do I define an Extension Method for IEnumerable which returns IEnumerable? The goal is to make the Extension Method available for

Answer 1

using System;
using System.Collections.Generic;

namespace ExtentionTest {
    class Program {
        static void Main(string[] args) {

            List BigList = new List() { 1,2,3,4,5,11,12,13,14,15};
            IEnumerable Smalllist = BigList.MyMethod();
            foreach (int v in Smalllist) {
                Console.WriteLine(v);
            }
        }

    }

    static class EnumExtentions {
        public static IEnumerable MyMethod(this IEnumerable Container) {
            int Count = 1;
            foreach (T Element in Container) {
                if ((Count++ % 2) == 0)
                    yield return Element;
            }
        }
    }
}