http://www.adelescorner.org/grammar/there_is/thereis.html
http://www.english-room.com/index.php?option=com_wrapper&Itemid=34
http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-7001.php
http://www.1-language.com/englishcourse/unit17_grammar_exs.htm
http://www.kico4u.de/english/uebungen/5klasse/thisare_ex2.htm
http://saberingles.com.ar/curso/lesson05/05.html
http://www.agendaweb.org/grammar/there_is_are-exercises.html:
