Which of the following is true about common costs?

Common costs are expenses that benefit multiple cost objects, such as departments or products, rather than being directly attributable to a single product or service. Therefore, these costs are often considered fixed in nature, as they do not change with the level of production for a specific product or service.

For example, a company might incur overhead costs such as utilities or salaries for management that serve multiple departments. Since these costs cannot be linked to just one product or service, they are classified as common costs. This distinction is important for budgeting and financial decision-making, as it impacts how resources are allocated and tracked across the organization.

The other options do not accurately represent the characteristics of common costs. They cannot be directly linked to a specific product or service, do not necessarily vary with production levels, and being relevant costs does not require them to be variable. Hence, option B clearly defines the nature of common costs.