Paper  bibtex   

@misc{Duolinguo:2017aa,
	Apple-Itunes-App = {app-id=570060128},
	Author = {Duolingo},
	Date = {2017},
	Date-Added = {2017-03-08 03:31:38 +0000},
	Date-Modified = {2017-04-17 12:29:33 +0000},
	Description = {Duolingo's bite-sized Spanish lessons are fun, easy, and 100% free. Practice online with language courses that are scientifically proven to work.},
	Google-Site-Verification = {nWyTCDRw4VJS_b6YSRZiFmmj56EawZpZMhHtKXt7lkU},
	Keywords = {ELE, CAPT, pronunciation teaching},
	Robots = {NOODP},
	Title = {Duolingo Spanish},
	Url = {https://www.duolingo.com/course/es/en/Learn-Spanish-Online},
	Viewport = {width=device-width, initial-scale=1.0},
	Yandex-Verification = {695573447ba029c6},
	Bdsk-Url-1 = {https://www.duolingo.com/course/es/en/Learn-Spanish-Online}}