Choice "C" is correct. Substantive tests are concerned with dollar amounts and consist of tests of details of transactions and balances and analytical procedures. The objective of tests of details of transactions performed as substantive tests is to detect material (dollar) misstatements in the financial statements.
Choice "a" is incorrect. Tests of details of transactions (performed as substantive tests) are used to evaluate management's assertions. While tests of details of transactions do help the auditor comply with GAAS, such compliance is not the primary objective of the tests.
Choice "b" is incorrect. Attaining assurance about the reliability of the information system relevant to financial reporting is an objective of tests of controls rather than of substantive tests.
Choice "d" is incorrect. Evaluation of the operating effectiveness of management controls is an objective of tests of controls rather than of substantive tests.