The financial statements of Z Co include a receivables balance of $20,000 which the auditors do not believe will be recovered. Materiality has been set at $100,000. There are no other unadjusted misstatements.What form of audit opinion would be issued by the auditor?
选项：

A:Adverse opinion ;
B: Unmodified opinion;
C: Disclaimer of opinion ;
D: Qualified opinion due to overstatement of receivables