An auditor's purpose in reviewing credit ratings of customers with delinquent accounts receivable most likely is to obtain evidence concerning management's assertions about:

Choice "a" is correct. Assertions about valuation and allocation deal with whether asset, liability, revenue, and expense components have been included in the financial statements at appropriate amounts, and any resulting valuation adjustments are appropriately recorded. For example, management asserts that trade accounts receivable included in the balance sheet are stated at net realizable value. Choice "b" is incorrect. Assertions about understandability and classification deal with whether financial information is appropriately presented and described, and disclosures are clearly expressed. Reviewing credit ratings of delinquent customers does not provide evidence about this type of assertion. Choice "c" is incorrect. Assertions about existence deal with whether assets, liabilities, and equity interest of the entity exist at a given date. Reviewing credit ratings of delinquent customers does not provide evidence about this type of assertion. Choice "d" 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 at a given date. Reviewing credit ratings of delinquent customers does not provide evidence about this type of assertion.