Preterit+Tense+Conjugation+Gramática

-AR verbs
http://www.youtube.com/watch?v=Jf7yEus4FwA http://www.youtube.com/watch?v=95heLa1taQA&feature=related

-ER verbs
http://www.youtube.com/watch?v=2i2GrTjDKFc&feature=related

-IR verbs
http://www.youtube.com/watch?v=L8kMZSFBrWI&feature=related