Wiangin, N., 		Sukkrong, J., 		Kaewkamjan, K., 		Phonkamjad, W., 		Promchitta, V., & 		Phanon, W.
2022 Jun 23.  Verb to be in Progressive Tense in American English. วารสารพุทธปรัชญาวิวัฒน์. [Online] 6:2