Choice "B" is correct. The function of cash receipts is part of the treasurer's department and should be separate from the role of writing off receivables. Failure to separate the recordkeeping function from the custodial function allows an individual to misappropriate cash and then cover up the theft by writing off the related receivable balance.
Choice "a" is incorrect. Internal controls in the revenue cycle typically relate to sales, receivables, and cash, not to the purchase and receipt of goods.
Choice "d" is incorrect. Internal controls in the revenue cycle typically relate to sales, receivables, and cash, not to inventory valuation.
Choice "c" is incorrect. If fictitious transactions in the revenue cycle are recorded, then the impact on revenues and receivables would be the same; either both would be overstated (the most likely case) or both would be understated.