What are transferred-in costs, as used in a process cost accounting system?

a. Labor that is transferred from another department within the same plant, instead of temporary workers hired from the outside.

b. Costs that have been incurred in a prior department, on units that have been moved into a subsequent department.

c. Supervisory salaries that are transferred from an overhead cost center to a production cost center.

d. Ending work-in-process inventory of a previous process that will be used in a succeeding process.