Practica de POR y PARA
http://www.quia.com/pop/54900.html?AP_rand=709704336
http://www.quia.com/rr/405736.html – rags to riches
http://www.quia.com/cz/6741.html?AP_rand=806798343 – por vs para cloze
http://www.quia.com/ba/104055.html – battleship
http://www.colby.edu/~bknelson/SLC/por_para1.php – paragraph with explanations or por and para
http://www.lrc.salemstate.edu/aske/webexercises/porpara01.htm – quiz with feedback