In these links you will find videos that explain quite clearly how plurals are build up in English:
https://www.youtube.com/watch?feature=player_detailpage&v=hrvq_YLOfXg&list=PL49586F62799A527D
https://www.youtube.com/watch?v=_3hauKIfi7g&list=PL49586F62799A527D
https://www.youtube.com/watch?feature=player_detailpage&v=2jrqNBc3U10&list=PL49586F62799A527D
With the following video, students will improve the pronuncation of the months:
https://www.youtube.com/user/breakthruchris
—————