Khumkongsuwan, K. , Hajisalah, S. , Janjaroon, A. and Watthanawisut, A. 2020. A STUDY OF MATTHAYOMSUKSA II STUDENTS’ PROOF ABILITIES IN PARALLEL-LINES TOPICS VIA THE CONSTRUCTIVIST LEARNING MODEL (CLM). Journal of Industrial Education. 19, 2 (Sep. 2020), 50–59.