Explanation:

- Marginal Cost refers to the cost of producing one additional unit of a good. It usually depends on variable costs.

- Option 1: Fixed Costs

- These are costs that do not change with the level of output, such as rent or salaries. They don't affect marginal cost.

- Option 2: Fixed and Variable Costs

- Combining fixed and variable costs does not define marginal cost, as fixed costs are not relevant to the additional unit cost.

- Option 3: Neither Fixed nor Variable Costs

- This is incorrect because marginal cost is influenced by variable costs, which change with production.

- Option 4: Variable Costs

- Marginal cost is tied to variable costs, as these vary directly with output.