Why Is Sales Figure Rather Than Cost of Goods Sold

Why is sales figure rather than cost of goods sold used when calculating the average days revenues in inventory (ADRI) ?

A) The value for COGS is not always comparable across firms due to accounting differences
B) COGS is not the driving variable behind the accumulation of inventory
C) Inventory is accumulated regardless of its COGS
D) There are three types of COGS: raw materials, work in progress, and finished goods.Since all are slightly different, using one or the other would make the calculations inaccurate.