Loy, C. L., and N. Abdul Wahab. “Teacher-Level and Context-Level Barriers to Using English As a Medium of Instruction: A Systematic Review”. Journal of Research, Policy & Practice of Teachers and Teacher Education, vol. 10, no. 2, Dec. 2020, pp. 77-98, doi:10.37134/jrpptte.vol10.2.6.2020.