Mengistu, F., Davtyan, A., Vorster, I., Xuecheng, D., Sembiring, E., GasmElseed, Y., & Bashir, A. (2004). System approach problem diagnosis and development strategies for a competitive mandarin to industry in the Karo highlands, North Sumatra, Indonesia. Uganda Journal of Agricultural Sciences, 9(1), 7–16. Retrieved from http://journal.naro.go.ug/index.php/ujas/article/view/192