Paper  bibtex   

@book{_spanish_2016,
	Author = {Duolingo},
	Date = {2016},
	Date-Modified = {2017-03-18 10:43:35 +0000},
	Keywords = {app, CAPT, ELE, pronunciation teaching},
	Title = {Spanish skills},
	Url = {https://www.duolingo.com/},
	Bdsk-Url-1 = {https://www.duolingo.com/}}