Concept:Different sources of farm power have different costs depending on fuel, equipment and maintenance.
Explanation:Power source I is the cheapest because it depends on crude tools and simple manual methods.
Manual farm power does not require fuel, electricity or expensive machinery.
The tools used are easy to obtain, simple to repair and have low maintenance costs.
In contrast, the other illustrated power sources like animals or machines require feeding, fuel or regular servicing, making them more expensive.
Therefore, the source of farm power illustrated as I gives the farmer the lowest cost of operation.
Answer:D. I
