Which of the following statements is correct?

a.		All other things being equal, if return on equity increases, the return on assets must have also increased.
b.		All other things being equal, the more efficiently a company utilizes its assets, the greater will be its return on investment.
c.		All other things being equal, if the gross margin decreases, the inventory turnover must have increased.
d		All other things being equal, if the number of days inventory held increases, the return on assets will increase.