Under which of the following circumstances would it be advisable for the auditor to confirm accounts payable with creditors?

Under which of the following circumstances would it be advisable for the auditor to confirm accounts payable with creditors?

a. Internal accounting control over accounts payable is adequate, and there is sufficient evidence on hand to minimize the risk of a material misstatement.
b. Confirmation response is expected to be favorable, and accounts payable balances are of immaterial amounts.
c. Creditor statements are not available and internal control over payables is unsatisfactory.
d. The majority of accounts payable balances are with associated companies.