Choice "C" is correct. In an audit of a nonissuer, the auditor is required to communicate both significant deficiencies and material weaknesses to management and those charged with governance.
Choice "d" is incorrect. The auditor is required to communicate significant deficiencies.
Choice "a" is incorrect. The auditor's report includes the definition of significant deficiencies and a list of such deficiencies noted, as well as the definition of material weaknesses and a list of such weaknesses noted.
Choice "b" is incorrect. Both significant deficiencies and material weaknesses are required to be communicated to management and those charged with governance.