Which of the following statements is TRUE?

a. When manufacturing overhead is applied to production, it is added to the Work in Process account.

b. Under a job-order costing system, the amount transferred from Work-in-Process to Finished Goods is the sum of the costs charged to all jobs completed and sold during the period.

c. If a company applies overhead to production on the basis of a predetermined rate, in the Manufacturing Overhead T-account a credit balance at the end of the period means that the estimated overhead cost was less than the actual overhead cost.

d. When raw materials are purchased, they are recorded as an expense.