Which of the following examples of fraud would be the most difficult to prevent and detect even if adequate separation of duties controls were designed and implemented?

A. An employee puts inventory behind the dumpster while unloading a suppliers delivery truck, and then picks up the inventory later in the day and takes it home

B. A credit manager issues credit cards to herself in the accounting office, and when the credit card balances are just under $1,000, she writes off the accounts as bad debt and issues new cards

C. A mail room employee steals a check received from a customer and destroys any related documentation, and then the staff accountant avoids entering record of it into the system

D. The accounts receivable clerk does not record sales invoices for friends or family so that they can receive free goods