Which of the following statements about the process costing system is incorrect?
a. In a process costing system, each processing department has work in process account.
b. In a process costing system, equivalent units are separately computed for materials and for conversion costs.
c. In a process costing system, overhead can be under- or overapplied just as in job-order costing.
d. In a process costing system, materials costs are traced to units of products.
