Ernita, Yuni, et al. “Analysis of Cocoa Industry Development Factor With System Approach in West Sumatera, Indonesia”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 36, no. 3, Oct. 2017, pp. 122-33, https://www.gssrr.org/JournalOfBasicAndApplied/article/view/8192.