Choice "C" is correct. For some assertions, analytical procedures are more effective and efficient at providing an appropriate level of assurance than are tests of details.
Choice "a" is incorrect. The objective of analytical procedures used in the planning stage of the audit is to assist in planning the nature, timing, and extent of auditing procedures to be performed.
Choices "d" and "b" are incorrect. The purpose of applying analytical procedures in the overall review stage of the audit is to assist the auditor in assessing the conclusions reached and the overall financial statement presentation. The overall review would also generally include consideration of the adequacy of evidence gathered in response to unusual or unexpected balances.