Final answer:
A fixed cost is best described as an expense that remains unchanged regardless of the level of output produced by a company.
Step-by-step explanation:
The question asks which description best fits a fixed cost. The correct answer is A. One that is unaffected by the level of output. Fixed costs refer to expenses that a company incurs that are not influenced by the volume of goods or services it produces. Examples include rent for a factory, the cost of essential machinery, and advertising to establish a brand. Whether the production is high or low, these costs remain constant in the short run. They are considered sunk costs and do not change with the production level, but rather are associated with the firm's fixed inputs like capital.