Explanation:

- Fuel Costs

- This is the correct answer. Fuel costs are a part of the operating costs for tractors. They are recurring expenses necessary for operating the machinery.

- Purchase Price

- The purchase price is a capital cost, not an operating cost. It is the initial expense of buying the tractor.

- Building Maintenance

- This is not related to the operation of tractors. It is a separate cost category for maintaining buildings.

- Employee Benefits

- While related to human resources, they are not directly part of operating a tractor.

- Marketing Expenses

- These are costs incurred to promote products and have no connection to the day-to-day operational costs of tractors.