http://www.azargrammar.com/assets/intermediate/FEGiGrammarSpeaks/chapter9/feg_ca_09_003.swf
http://www.azargrammar.com/assets/intermediate/FEGiGrammarSpeaks/chapter9/feg_ca_09_002.swf
http://suz.digitaleschulebayern.de/english/grammar/comp1.htm
http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-28752.php
http://www.english-4u.de/comparison_ex1.htm
http://www.montsemorales.com/gramatica/Comparative.htm
http://www.bbc.co.uk/worldservice/learningenglish/youmeus/quiznet/newquiz62.shtml
http://www.englishexercises.org/makeagame/viewgame.asp?id=2065