Choice "A" is correct. The auditor is not required to search for significant deficiencies (but any that are identified should be reported).
Choice "b" is incorrect. Material weaknesses are deficiencies in internal control such that there is a reasonable possibility that a material misstatement of the entity's financial statements will not be prevented or detected/corrected on a timely basis. Material weaknesses are important enough to merit attention by those charged with governance, and therefore all material weaknesses are in fact significant deficiencies.
Choice "d" is incorrect. The auditor is required to communicate to those charged with governance all significant deficiencies that he or she observes during the audit.
Choice "c" is incorrect. The auditor should not indicate to management that no significant deficiencies were noted during the audit, as this might cause misinterpretation of the auditor's responsibility in such cases.