Choice "B" is correct. Assertions about rights and obligations deal with whether assets are the rights of the entity and liabilities are the obligations of the entity. Errors reported by customers might indicate receivables for which the company has no right of collection.
Choices "d" and "a" are incorrect. Assertions about classification and understandability deal with whether financial information is appropriately presented and described, and disclosures are clearly expressed. Follow-up of errors reported by customers would not impact the proper presentation, description, and disclosure of accounts receivable in the financial statements.
Choice "c" is incorrect. Assertions about rights and obligations deal with whether assets are the rights of the entity and liabilities are the obligations of the entity. Errors reported by customers might indicate receivables for which the company has no right of collection.