The correct answer is: B. process costing.
Boiler house costing is an example of process costing because it is a type of costing that is used to track the costs of a process that produces a large number of identical or similar units of output. In a boiler house, the process is the production of steam, and the units of output are the pounds of steam produced.
Operation costing is a type of costing that is used to track the costs of a specific operation or activity. For example, an operation costing system might be used to track the costs of producing a specific product or service.
Service costing is a type of costing that is used to track the costs of providing a service. For example, a service costing system might be used to track the costs of providing a customer service call center.
None of these is not a valid answer choice.