Answer:
The correct answer is letter "A": salary of a production supervisor.
Step-by-step explanation:
Variable Costs vary depending on the company's production volume. Variable costs go up when the company produces more goods or services and go down when it produces fewer goods or services. This is compared to fixed costs which do not change in proportion to production volume.
Direct materials, production supplies, commissions, and fees are examples of variable costs. The salary of a production supervisor would fall under this category.