4OSGUTHORPE R T & GRAHAM C R. Blended learning environ- ments: definitions and directions [ J]. Quarterly Review of Dis- tance Education, 2003, 4 (3) : 227 -233.
5KONSTAN J A, WALKER J D, BROOKS D C, et al. Teaching recommender systems at large scale: evaluation and lessons learn- ed from a hybrid MOOC [ C ]//The committee of the ACM confer- ence on Learning@ scale. Proceedings of the first ACM conference on Learning@ scale. New York: ACM, 2014:61 -70.
6TOMKIN J H & CHARLEVOIX D. Do professors matter: using an a/b test to evaluate the impact of instructor involvmnent on MOOC student outcomes [ C]//The committee of the ACM con- ference on Learning@ scale. Proceedings of the first ACM confer- ence on Learning@ scale. New York: ACM, 2014 : 71 -78.