Tài liệu tham khảo WikiPedia: Google_Duo http://www.androidguys.com/2016/05/18/knock-knock-... http://www.androidpolice.com/2016/08/18/duo/ http://arstechnica.com/gadgets/2016/08/googles-lau... http://www.cnet.com/news/googles-duo-is-another-vi... http://www.techradar.com/news/phone-and-communicat... http://www.theverge.com/2016/5/18/11690728/google-... https://duo.google.com/ https://www.theguardian.com/technology/2016/aug/16... https://googleblog.blogspot.co.uk/2016/05/allo-duo... https://googleblog.blogspot.co.uk/2016/08/meet-goo...
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