Option C is correct because lenders and suppliers are the parties who extend credit to the firm. The average payment period indicates how long the firm takes to pay its trade payables (creditors and bills payable). Suppliers, being the ones who provide goods on credit, are directly concerned with the firm's bill-paying patterns as it affects their cash flows and credit decisions. Similarly, lenders who advance money to the business want to assess whether the firm pays its obligations on time. This ratio helps them evaluate the creditworthiness and payment behaviour of the firm before extending further credit.