Under what condition is the Registrar prohibited from investigating a complaint?

The correct choice is that the Registrar is prohibited from investigating a complaint under the condition of "none of the above," meaning that there are no specific statuses such as being suspended, expired, or voluntarily surrendered that inherently prevent the Registrar from conducting an investigation.

In the field of regulatory practice, typically, complaints can still be investigated regardless of the status of the subject involved. For example, even if a license is expired or voluntarily surrendered, there could be ongoing concerns about public safety or professional conduct that the Registrar needs to address. Therefore, the role of the Registrar encompasses the duty to ensure compliance and accountability regardless of the individual's license status. This approach helps maintain the integrity of the profession and protects the public interest.

The choices indicating "suspended," "expired," or "voluntarily surrendered" suggest that these conditions would halt investigations, which is not reflective of the typical regulatory practice, thereby reinforcing that none of these conditions would prevent the Registrar from investigating a complaint.