Final answer:
The correct response is option d. Unusual, as personal, organizational, and external are the types of impairments described by the GAO, whereas 'unusual' is not one of these types. The correct option is c.
Step-by-step explanation:
The Independence standards of the GAO (Government Accountability Office) for audits, in accordance with generally accepted government auditing standards, describe three types of impairments to independence, which are personal, organizational, and external impairments.
The option 'unusual' does not represent a type of impairment as defined by the GAO standards. Therefore, the correct answer to the question is option d. Unusual.
External impairments occur when an auditor is influenced by forces or parties outside of the audited entity that may impact the auditor's ability to perform work objectively.
Personal impairments involve relationships or biases that auditors might have that affect their independence. Organizational impairments relate to the placement of the audit organization within the government or other circumstances that could impact independence. The correct option is c.