Sales at Loggins Corp declined compared to those of the preceding year. In an effort to improve the financial statements, the vice president of finance obtained a supply of blank shipping notices on which she fabricated 100 fictitious shipments. She submitted the fictitious documents to the billing department for billing. Which of the following controls would help solve this problem: a) Reconcile bank account monthly b) Check for authorized prices, terms, freight, and discounts c) Confirm customer accounts regularly d) Independent billing authorization