Explanation:

Setup costs refer to the expenses incurred in preparing the machines, equipment, and tools for a specific production task. These costs are typically one-time expenses that are associated with the setup of a production line. The following are the details of the options given in the question:

Labour cost of setting up machines:
- When a production line is set up, it requires skilled labor to install and configure the machines, equipment, and tools for the specific task. This cost is included in the setup cost.

Ordering cost of raw material:
- Ordering cost of raw material refers to the cost incurred in placing and receiving an order of raw material. It includes the cost of communication, transportation, and inspection of the material. This cost is not included in the setup cost.

Maintenance cost of the machines:
- Maintenance cost of the machines refers to the cost incurred in keeping the machines, equipment, and tools in good working condition. This cost is not included in the setup cost, as it is an ongoing expense that is incurred throughout the production process.

Cost of processing the work piece:
- Cost of processing the work piece refers to the cost of converting the raw material into a finished product. This cost is not included in the setup cost, as it is an ongoing expense that is incurred throughout the production process.

Conclusion:

In conclusion, the correct answer to the given question is option 'C' i.e., Maintenance cost of the machines. Setup costs only include one-time expenses incurred in preparing the machines, equipment, and tools for a specific production task. Maintenance cost is an ongoing expense that is incurred throughout the production process.