http://cerquella.com/bilingual/deploy2/Unit3/grammar_1.html
http://www.adelescorner.org/grammar/past_cont/past_cont_neg.html
http://www.kico4u.de/english/uebungen/aktiv/pastprogressive.htm
http://www.perfect-english-grammar.com/past-continuous-exercise-4.html
http://www.eflnet.com/grammar/yesnopastprog.php
http://www.english-grammar-lessons.com/pastcontinuous/exercise1.swf
http://www.english-grammar-lessons.com/pastcontinuous/exercise3.swf
http://www.adelescorner.org/grammar/past_cont/past_cont_2.html
http://www.ego4u.com/en/cram-up/grammar/past-progressive/exercises?04
http://www.eslkidsworld.com/Interactive%20games/past%20continuous%20quiz.html