Choice "A" is correct. Because timely communication may be important, the auditor may choose to communicate significant deficiencies during the course of the audit rather than after the audit is concluded.
Choice "d" is incorrect. The auditor is not obligated to search for significant deficiencies.
Choice "b" is incorrect. All material weaknesses are significant deficiencies, but not all significant deficiencies are material weaknesses.
Choice "c" is incorrect. Because of the potential for misinterpretation, the auditor should not issue a written report representing that no significant deficiencies were noted during the audit.