http://www.ego4u.com/en/cram-up/grammar/simpre-prepro
http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/simcon1.htm
http://www.perfect-english-grammar.com/present-simple-present-continuous-2.html
http://www.englishexercises.org/makeagame/viewgame.asp?id=1438
http://www.aulafacil.com/Ingejerc/Lecciones/Ejerc18.htm
http://www.englisch-hilfen.de/en/exercises/tenses/simple_present_progressive2.htm
http://www.englishexercises.org/makeagame/viewgame.asp?id=4927
http://www.englishexercises.org/makeagame/viewgame.asp?id=796
http://www.englishexercises.org/makeagame/viewgame.asp?id=1098