[Wang, Xiang] Beijing Normal Univ, Fac Educ, Beijing, Peoples R China.
[Sun, Di] Dalian Univ Technol, Fac Human & Social Sci, Dalian, Liaoning, Peoples R China.
[Cheng, Gang] Open Univ China, Dept Informat Technol, Beijing, Peoples R China.
[Cheng, Gang] Minist Educ, Engn Res Ctr Integrat & Applicat Digital Learning, Beijing, Peoples R China.
[Luo, H; Luo, Heng] Cent China Normal Univ, Sch Educ Informat Technol, Wuhan, Hubei, Peoples R China.