Reforzamiento primeros medios

http://www.ego4u.com/en/cram-up/grammar/present-perfect-simple/exercises?03

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

http://www.ego4u.com/en/cram-up/tests/present-perfect-simple-1

http://www.englisch-hilfen.de/en/complex_tests/present_perfect1/index.php?action=start2&aufgid=12&Submit=Answer+a+special+part

http://www.ego4u.com/en/cram-up/vocabulary/since-for

http://www.englishexercises.org/makeagame/viewgame.asp?id=1394