Choice "A" is correct. Failure to disclose information that is required by GAAP is a departure from GAAP. Departures from GAAP result in a qualified or an adverse opinion.
Choice "c" is incorrect. If the auditor is unable to observe physical inventory and is unable to become satisfied through alternative means, that is a scope limitation. Scope limitations result in either a qualified opinion or a disclaimer of opinion.
Choice "b" is incorrect. The auditor can report on one financial statement and not the others. This does not preclude issuance of an unmodified opinion.
Choice "d" is incorrect. 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 (after the opinion paragraph in the unmodified report) to reflect that conclusion.