Choice "B" is correct. The auditor should obtain a sufficient understanding of the entity and its environment, including its internal control, to plan the audit of the entity's financial statements.
Choice "c" is incorrect. The representation letter is not obtained until the end of the audit.
Choice "a" is incorrect. Informing those charged with governance of significant deficiencies in internal control generally occurs during or at the completion of the audit. It is not required before completion of the audit plan.
Choice "d" is incorrect. The search for unrecorded liabilities typically takes places after year-end, while the audit plan is prepared during planning. Information obtained from the search is not needed to finalize the audit plan.