What are "ofensivas"? I don't understand it...
"Ofensivas" are the sequence of days that you have if you keep training, practicing or learning here on Duolingo daily (I'm learning here too, so I don't know exactly how to use some prepositions, dude. Please, don't notice these little mistakes).
If you don't practice at least one day (I think so, I don't have sure), your number of "ofensiva" will fall.
Não sei exatamente, mas eu fiz uma breve pesquisa pelo sistema de busca do Duolingo e encontrei alguns tópicos, talvez te ajude, não peguei todos porque eram muitos, mas, segue alguns:
http://www.duolingo.com/comment/700744 http://www.duolingo.com/comment/773125 http://www.duolingo.com/comment/834560 http://www.duolingo.com/comment/954395 http://www.duolingo.com/comment/540968 http://www.duolingo.com/comment/599191 http://www.duolingo.com/comment/637293 http://www.duolingo.com/comment/680260