1. See the examples:
http://www.theyellowpencil.com/gramacomparativos.html#
2. Exercise of comparatives:
http://www.learnenglishfeelgood.com/sp/adjetivos-comparativos1.html
3. Another exercise of comparatives:
http://www.inglesmadrid.com/comparativo-30c.htm
4. Last exercise of comparatives:
http://www.englishexercises.org/exercise.asp?id=2065#a
