a, an, the 

http://ingles.about.com/od/Partes-de-la-oracion/fl/Los-sustantivos-o-nombres-en-ingles-noun-parte-2.htm

http://www.really-learn-english.com/english-grammar-articles-es.html

Exercises

http://www.vitutor.com/gramatica_inglesa/articles/articles_ej4.html

Prepositions of place

http://www.grammar.cl/rules/prepositions-of-place.htm

Exercises

http://www.englishexercises.org/makeagame/viewgame.asp?id=597