Choice "A" is correct. The auditor relies on substantive tests to achieve audit objectives related to particular assertions. Analytical procedures are one type of substantive procedure.
Choice "c" is incorrect. CPA firms performing audits are required to adhere to a system of quality control, but adhering to such a system does not directly help the firm achieve specific audit objectives.
Choice "d" is incorrect. Audit documentation is used to record the results of audit procedures that have been performed to achieve audit objectives. Mere preparation of audit documentation does not achieve audit objectives.
Choice "b" is incorrect. Increasing the level of detection risk does not enable the auditor to achieve audit objectives related to a particular assertion.