Ryan, M., Abeyratne, F., & Farrington, J. (1981). Animal draught: The economics of revival. Agrarian Research and Training Institute.
Lua i Stíl Chicago (17ú heag.)Ryan, M., Fredrick Abeyratne, agus Joseph Farrington. Animal Draught: The Economics of Revival. Colombo, Sri Lanka: Agrarian Research and Training Institute, 1981.
Lua MLA (8ú heag.)Ryan, M., et al. Animal Draught: The Economics of Revival. Agrarian Research and Training Institute, 1981.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.