http://www.helpforenglish.cz/gramatika/pridavna-jmena/stupnovani/c2006080103-Stupnovani-pridavnych-jmen-v-anglictine.html
exercise:
http://www.helpforenglish.cz/gramatika/pridavna-jmena/stupnovani/c2006080302--C-Stupnovani--a-porovnavani--cviceni-.html
http://www.learnenglishfeelgood.com/english-comparative-superlative1.html
http://www.englisch-hilfen.de/en/exercises/adjectives_adverbs/adjectives_comparison_as_as.htm