Choice "C" is correct. If, after considering identified conditions and events and management's plans, the auditor concludes that substantial doubt about the entity's ability to continue as a going concern for a reasonable period of time remains, the audit report should include an emphasis-of-matter paragraph to reflect that conclusion.
Choice "d" is incorrect. Reporting on just the balance sheet is acceptable provided access to financial information is not limited. Such reporting does not require an emphasis-of-matter paragraph.
Choice "b" is incorrect. If the auditor concludes that management's estimate is unreasonable and that its effect is to cause the financial statements to be materially misstated, the auditor should express a qualified or an adverse opinion.
Choice "a" is incorrect. Restrictions on the scope of the audit, whether imposed by the client or by circumstances, may require the auditor to qualify or to disclaim an opinion.