Links:
http://www.englisch-hilfen.de/en/exercises/questions/be.htm (to be questions)
http://www.englisch-hilfen.de/en/exercises/tenses/simple_present_s2.htm (3rd person rule)
http://www.englisch-hilfen.de/en/exercises/tenses/simple_present_s.htm (3rd person rule)
http://english-zone.com/verbs/thereisare1.html (there is or there are)
