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

(a). Labour that is transferred from another department within the same plant instead of hiring temporary workers from the outside.

(b). Cost of the production of a previous internal process that is subsequently used in a succeeding internal process 

(c). Supervisory salaries that are transferred from an overhead-cost centre to a production-cost centre 

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