The correct answer is D. Job costing.
Job costing is a type of costing system that is used to track the costs of individual jobs or projects. It is often used in industries where each job or project is unique, such as construction, manufacturing, and interior decoration.
In job costing, each job or project is assigned a unique number or code. The costs of materials, labor, and overhead are then tracked for each job or project. This information is used to calculate the cost of each job or project, which can then be used to set prices and determine profitability.
Contract accounting is a type of costing system that is used to track the costs of construction projects. It is similar to job costing, but it is designed to track the costs of large, complex projects that may take months or even years to complete.
Operating costing is a type of costing system that is used to track the costs of ongoing operations. It is often used in industries where there are a large number of similar products or services, such as manufacturing and retail.
Process costing is a type of costing system that is used to track the costs of manufacturing processes. It is often used in industries where there are a large number of identical products or services, such as oil refining and chemical manufacturing.
In conclusion, job costing is the best method of costing for interior decoration because it is designed to track the costs of individual jobs or projects. This information is used to calculate the cost of each job or project, which can then be used to set prices and determine profitability.