A three-way match is a process of verifying that a purchase order, a goods receipt and an invoice are consistent before making a payment1. A three-way match ensures that the organization only pays for the goods or services that it ordered and received, and that the prices and quantities are accurate. A three-way match can prevent errors, fraud and overpayments in the accounts payable process.
An IS auditor should use a purchase order when verifying a three-way match has occurred in an enterprise resource planning (ERP) system. A purchase order is a document that authorizes a purchase transaction and specifies the items, quantities, prices and terms of the order2. A purchase order is the first document in the three-way match process, and it serves as the basis for comparing the goods receipt and the invoice. An IS auditor can use a purchase order to check if the ERP system has correctly recorded, matched and approved the three documents before making a payment.
The other options are not as useful for verifying a three-way match. A bank confirmation is a document that verifies the balance and activity of a bank account3. A bank confirmation can be used to confirm that a payment has been made or received, but it does not provide information about the details of the purchase transaction or the three-way match process. A goods delivery notification is a document that informs the buyer that the goods have been shipped or delivered by the seller4. A goods delivery notification can be used to track the status of the delivery, but it does not provide information about the quantity or quality of the goods or the invoice amount. A purchase requisition is a document that requests authorization to purchase goods or services from a specific supplier2. A purchase requisition can be used to initiate the purchasing process, but it does not provide information about the actual purchase order, goods receipt or invoice.
References:
Bank Confirmation - Overview, How It Works, Importance3
What is Goods Delivery Note? | Definition and Example4
What Is Three-Way Matching and Why Is It Important? | NetSuite1
Enterprise Resource Planning (ERP) - Definition, Types, Uses2

When an employee exploits avulnerability, the most appropriate audit is aforensic audit, as it focuses oninvestigating and documenting security incidentsfor legal or disciplinary action.
Option A (Incorrect):Acompliance auditensures adherence to policies but does not investigate incidents in detail.
Option B (Incorrect):Application security testinghelps identify vulnerabilities but does not addressemployee misuse.
Option C (Correct):Aforensic auditgathersdigital evidence, determines how the exploit occurred, and ensures legal compliance in the investigation.
Option D (Incorrect):Penetration testingidentifies weaknesses but does notanalyze past incidents.
Reference:ISACA CISA Review Manual -Domain 5: Protection of Information Assets- Covers forensic investigations, digital evidence collection, and security incident response.

Unauthorized changes can be moved into production is the best concern that is addressed by securing production source libraries. Production source libraries contain the source code of programs that are used in the production environment. Securing production source libraries means implementing access controls, change management procedures, and audit trails to prevent unauthorized or improper changes to the source code that could affect the functionality, performance, or security of the production programs. The other options are less relevant concerns that may not be directly addressed by securing production source libraries, but rather by other controls such as program approval, version control, or change testing. References:
CISA Review Manual (Digital Version), Chapter 4, Section 4.2.3.21
CISA Review Questions, Answers and Explanations Database, Question ID 213

The best answer is C. Operate in fail-secure mode.
If the goal is to prevent unauthorized entry during a power outage, the doors should remain locked when power fails. That is exactly what fail-secure operation is intended to do. Alarming and monitoring may detect an issue, but they do not themselves prevent entry. Physical key backup may help authorized access, but it does not address the primary requirement of staying secure during loss of power.
So the strongest answer is fail-secure, because it directly preserves physical access control during an outage.
References (Official ISACA):
* ISACA physical security and access-control terminology resources support layered protection of facilities.

The best audit evidence that a firewall is configured in compliance with the organization's security policy is to review the rule base. The rule base is a set of rules that defines the criteria for allowing or denying network traffic through the firewall. By reviewing the rule base, the auditor can verify if the firewall configuration matches the security policy requirements and objectives. Analyzing how the configuration changes are performed, analyzing log files, and performing penetration testing are useful audit techniques, but they do not provide direct evidence of the firewall configuration compliance. References: CISA Review Manual (Digital Version)1, page 383.