In a segmented income statement, which of the following statements is true?
  a.  Segment margin is greater than contribution margin.
  b.  Common fixed expenses must be allocated to each segment.
  c.  Contribution margin is equal to sales less all variable and direct fixed expenses of a segment.
  d.  Segment margin is equal to contribution margin less direct fixed expenses.
  e.  Segment margin is equal to contribution margin less direct and common fixed expenses.