1. National Engineering Research Center for E-learning, Central China Normal University, Wuhan, People’s Republic of China
2. 17Zuoye, Beijing, China
3. Advanced Innovation Center for Future Education, Beijing Normal University, Beijing, People’s Republic of China
4. Key Lab of Intelligent Information Processing of Chinese Academy of Science (CAS), Institute of Computing Technology, CAS, Beijing, China
5. University of Chinese Academy of Sciences, Beijing, China