Explicação com vídeo: https://www.youtube.com/watch?v=ZOHiSlqPR94
Link 1: http://www.autoenglish.org/gr.since.pdf
Link 2: http://www.macmillaninspiration.com/original/files/2010/07/INSP3_ws9.pdf
Link 3: http://www.ecenglish.com/learnenglish/lessons/for-or-since
