1. Faculty of Education, Beijing Normal University, Beijing, China
2. Center for Research on Technology-Enhanced Language Education, Beijing University of Posts and Telecommunications, Beijing, China
3. Teaching Affairs Department, Shenzhen Longhua Experimental School, Shenzhen, China
4. Department of Applied Foreign Languages, National Yunlin University of Science and Technology, Taiwan
5. Language Technologies Institute and Human-Computer Interaction Institute, Carnegie Mellon University, Pittsburgh, PA, USA