Which of the following statements is true?
  a.  Job-order costing is used only in manufacturing firms.
  b.  The job cost sheet is subsidiary to the work-in-process account.
  c.  Job-order costing is simpler to use than process costing because the recordkeeping requirements are less.
  d.  Process costing is used only for services.
  e.  All of the above are true.