What is primarily included in fixed costs?

Fixed costs are expenses that do not change with the level of production or sales volume. They remain constant regardless of the quantity of goods or services produced within a specific time frame. Examples of fixed costs include monthly expenses that are necessary for business operations, such as rent for premises and salaries of employees. These expenses are typically incurred no matter how much the company produces or sells, making them a crucial aspect of budgeting and financial management.

In contrast, the other options refer to costs that are variable or dependent on changes in production or market conditions. For instance, costs that fluctuate with production volume or expenses for materials and inventory vary based on the business's output levels and are not fixed. Similarly, costs dependent on customer demand can change significantly based on sales levels or market trends. Therefore, the correct answer highlights the nature of fixed costs as consistent expenditures that support core operations regardless of business activity.