Choice "B" is correct. Applying substantive tests to the details of asset and liability accounts as of an interim date increases risk, as it is possible that errors will occur between the date of interim testing and the balance sheet date. For this reason, the auditor generally selects for interim examination only accounts that are reasonably predictable with respect to amount, relative significance, and composition, and must also identify procedures sufficient to extend interim conclusions to year-end.
Choice "c" is incorrect. The use of statistical sampling methods is not affected by the timing of audit procedures.
Choice "a" is incorrect. Applying substantive tests to the details of asset and liability accounts as of an interim date increases risk, but it does not require all such tests to be reperformed. Instead, the auditor should perform procedures designed to extend the interim conclusions to year-end. Such procedures should be less in scope than the initial procedures performed at interim; otherwise, it would make more sense to have simply applied the more extensive tests at year-end in the first place.
Choice "d" is incorrect. Generally, accounts selected for interim examination should be reasonably predictable with respect to amount, relative significance, and composition. Rapidly changing economic conditions might affect the valuation, significance, or composition of certain assets or liabilities, and therefore would make testing at interim less likely.