e-graphy/bibliography

http://www.curso-ingles.com/aprender/cursos/nivel-avanzado/verb-tenses-present-perfect/present-perfect

http://www.curso-ingles.com/aprender/cursos/nivel-intermedio/verb-tenses-future/future-simple

http://www.curso-ingles.com/aprender/cursos/nivel-avanzado/verb-tenses-present-perfect/present-perfect-continuous

http://www.curso-ingles.com/aprender/cursos/nivel-intermedio/verb-tenses-past/past-continuous

http://www.curso-ingles.com/aprender/cursos/nivel-intermedio/verb-tenses-past/past-simple

http://www.curso-ingles.com/aprender/cursos/nivel-basico/verb-tenses-present/present-continuous

http://www.curso-ingles.com/aprender/cursos/nivel-avanzado/verb-tenses-past-perfect/past-perfect

http://www.curso-ingles.com/aprender/cursos/nivel-basico/verb-tenses-present/present-simple