This Question Requires Knowledge About Specific Account Balance Assertions, General

This question requires knowledge about specific account balance assertions, general audit procedures, and trade accounts payable.
You are assigned to audit trade accounts payable at Green Corporation, whose business is wholesale and retail trade. Green purchases products from 1,000-2,000 manufacturers and sells the products to its retail and wholesale customers. The general ledger shows a trade accounts payable balance as of the balance sheet date in the amount of $42 million (the balance comprises 70% of current liabilities, 50% of total liabilities, and 35% of total liabilities and shareholders' equity). Green's accountants post summary entries from the purchases journal and from the cash disbursements journal to the accounts payable control account each month. The accounts payable manager gave you a detailed trial balance that lists all the recorded, unpaid invoices (recording date, vendor name, vendor invoice number, invoice date, and amount) subtotalled by vendor.
Other members of the audit team have already decided to assess control risk at maximum for accounts payable. The engagement manager gave you last year's audit working papers and told you not to use the audit program from last year because it was no longer appropriate. The first part of your assignment is to write the audit program for the audit of Green's trade accounts payable.
Required:
For each of the general assertions EXISTENCE, COMPLETENESS, and VALUATION, write two or more specific audit procedures designed to produce appropriate evidence about Green's trade accounts payable balance.