Kusin, J., Sinaga, H. S. R., Khoma, J., Houtkooper, J. M., & Renqvist, U. (1981). The preschool child in Suka Village, North Sumatera. Paediatrica Indonesiana, 21(9-10), 181-91. https://doi.org/10.14238/pi21.9-10.1981.181-91