Mixed exercises

PRESENT PERFECT AND PAST SIMPLE

http://www.englishexercises.org/makeagame/viewgame.asp?id=1496

http://www.perfect-english-grammar.com/past-simple-present-perfect-4.html

http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/ppvpast1.htm

PRESENT SIMPLE

http://www.englisch-hilfen.de/en/exercises/tenses/simple_present_mix.htm

http://www.agendaweb.org/verbs/present_simple-exercises.html

http://www.isabelperez.com/happy/tenses/present_simple.htm

PAST SIMPLE

http://www.agendaweb.org/verbs/past_simple-exercises.html

http://www.ego4u.com/en/cram-up/grammar/simple-past/exercises

http://www.ego4u.com/en/cram-up/grammar/simple-past

http://www.myenglishpages.com/site_php_files/grammar-exercise-simple-past.php