In Comparison of 2010 to 2009 Performance,Watson Company's Inventory Turnover

In comparison of 2010 to 2009 performance,Watson Company's inventory turnover decreased substantially,although sales and inventory amounts were essentially unchanged.
Required:
During a corporate meeting you heard the following managers postulate why the decreased inventory turnover ratio happened.Which statement best explains the decreased inventory turnover ratio and why?
a.The marketing manager said: The decreased inventory turnover ratio is due to an increase in the cost of goods sold.
b.The operations manager said: The decreased inventory turnover ratio is due to increased gross profit percentage.
c.The credit manager said: The decreased inventory turnover ratio is due to a decrease in the accounts receivable turnover.
d.The shipping manager said: The decreased inventory turnover ratio is due to decreased total asset turnover.