Classify each of the following as direct or indirect with respect to traceability to product and as variable or fixed with respect to whether the costs fluctuate in total as volume of production changes over wide ranges. Explain your classifications.
1. The cost of components that are assembled into a final product
2. The cost of supplies consumed when maintenance is performed on machines
3. The wages of machine operators who work on only one product
4. The cost of training mechanics who service processing machinery