Which of the following costs remain unchanged as activity levels change?

Fixed costs are the correct answer because they remain constant regardless of changes in activity levels within a relevant range. These costs do not fluctuate with the volume of production or sales and include expenses such as rent, salaries of permanent staff, and insurance. They are incurred regardless of how much activity occurs within a business.

In contrast, variable costs change in direct proportion to the activity level. For example, raw material costs vary with the number of products produced. Direct costs are expenses that can be directly traced to specific units of production, which can include variable costs as well as fixed overheads related to production. Indirect costs, often lumped together as part of overheads, may also include fixed elements, but they do not have the characteristic of remaining unchanged across all activity levels as fixed costs do. Therefore, fixed costs are the only type that consistently does not change with varying levels of activity.