Concept:Farm power sources are the means used to do farm work, while implements are tools used on the farm.Explanation:Wind, bull, and tractor all provide power for farm operations such as milling, ploughing, or hauling.A plough is an implement or tool, not a source of power. It is pulled by a bull or tractor to work on the land.Thus, the option that is not a source of farm power is the plough.Answer:D. Plough