Before applying principal substantive tests to the details of asset and liability accounts at an interim date, the auditor should

a. Assess the difficulty in controlling incremental risk.

b. Investigate significant fluctuations that have occurred in the asset and liability accounts since the previous balance-sheet date.

c. Select only those accounts that can effectively be sampled during the year- end audit work.

d. Consider the tests of controls that must be applied at the balance-sheet date to extend the audit conclusions reached at the interim date.