PRESENT TENSES

PRESENT SIMPLE AND PRESENT CONTINUOUS

http://www.ego4u.com/en/cram-up/grammar/simpre-prepro/exercises

http://www.ego4u.com/en/cram-up/grammar/simpre-prepro/exercises?ex12

http://www.englishpage.com/verbpage/verbs1.htm

PRESENT PERFECT

FORMATION: http://www.ego4u.com/en/cram-up/grammar/present-perfect-simple/exercises

PRESENT PERFECT (ALREADY/ YET/STILL/EVER...) http://www.eclecticenglish.com/grammar/PresentPerfect1C.html

http://perso.wanadoo.es/autoenglish/gr.presper.i.htm

http://www.1-language.com/englishcoursenew/unit55_grammar_exs.htm

PRESENT PERFECT (FOR/SINCE): http://www.eclecticenglish.com/grammar/PresentPerfect1D.html

PRESENT PERFECT VERSUS PRESENT PERFECT CONTINUOUS

http://www.englishpage.com/verbpage/verbs7.htm

http://www.englishpage.com/verbpage/verbs8.htm