Which of the following is an example of a step-fixed cost?

a.cost of disposable gowns used by patients in a hospital

b.cost of soaking solution to clean jewelry (Each jar can soak 50 rings before losing effectiveness.)

c.cost of tuition at $300 per credit hour up to 15 credit hours (Hours taken in excess of 15 hours are free.)

d.cost of disposable surgical scissors, which are purchased in increments of 100