PRESENT SIMPLE ( Disponibles en Agenda web )
http://www.agendaweb.org/verbs/present-simple/index.html
http://www.agendaweb.org/exercises/verbs/present-simple.htm
http://www.agendaweb.org/exercises/verbs/present-forms.htm
http://www.englishmaven.org/HP6/Present%20Tense%20Exercise%206.htm
http://www.montsemorales.com/gramatica/PresSimp1.htm
http://www.really-learn-english.com/simple-present-exercises.html#01
PAST SIMPLE
http://www.myenglishpages.com/site_php_files/grammar-exercise-simple-past.php
