For effective internal control purposes, the vouchers payable department generally should

(a) stamp, perforate, or otherwise cancel supporting documentation after payment is mailed.

(b) ascertain that each requisition is approved as to price, quantity, and quality of an authorized employee.

(c) obliterate the quantity ordered on the receiving department copy of the purchase order.

(d) establish the agreement of the vendor's invoice with the receiving report and purchase order.