What does days' sales outstanding tell you? 

 a. It provides an indication of how many days, on average, it takes for customers to receive their invoices. 

b. It provides an indication of how many days, on average, it takes for customers to pay their invoices. 

c. It provides an indication of how many days, on average, it takes for the company to sell its inventory. 

d. It provides an indication of how many days, on average, it takes for the company to pay its accounts due.