Confidentiality

Auditor would have legal (mandatory) obligation to disclose A/D under AML/Proceeds of crime legislation. I don't have Kaplan materials to know why B is considered correct but I imagine what it is saying is that if an NGO has power to demand disclosure - the auditor may disclose voluntarily rather than wait for that power to be exercised.

Because statutory/legal duties are mandatory/compulsory - the auditor doesn't have any discretion to choose or elect whether or not to disclose (the meaning of voluntary).