Answer: d. Payment to a supplier
Explanation:
Option "a" is an acquisition of debt, which is not a source of cash.
Option "b" is purchase of inventory, which is not a source of cash, but uses cash.
Option "c" is granting credit to a customer, which is not a source of cash, but uses cash.
Option "e" is repurchase of common stock, which is not a source of cash, but uses cash.
Option "d" is payment to a supplier, which is a source of cash.