http://www.ego4u.com/en/cram-up/grammar/past-progressive
www.englishgrammarsecrets.com/pastcontinuous/exercise3.swf
http://inglesnanet.com/grammar/pastscon.htm
http://www.englishclub.com/grammar/verb-tenses_past-continuous-quiz.htm
http://www.eflnet.com/grammar/pastprog.php
http://www.english-grammar-lessons.com/pastcontinuous/exercise3.swf
http://www.englishgrammarsecrets.com/pastcontinuous/exercise2.swf
http://www.englishgrammarsecrets.com/pastcontinuous/exercise3.swf
http://ww2.college-em.qc.ca/prof/epritchard/sawasing.htm
http://www.members.iinet.net.au/~adelegc/grammar/past_cont/past_cont_neg.html
http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-8801.php
http://www.english-grammar-lessons.com/pastcontinuous/exercise2.swf
http://personales.ya.com/mjandres/archivos/ptsc1.htm
http://www.english-4u.de/past_prog_ex2.htm
http://www.oup.com/elt/global/products/headway/preint/a_grammar/unit03/hwy_preint_unit03_1/
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