Final answer:
Option d, where the auditor traces transactions from purchase order to financial statements, best represents a walkthrough, as it involves a comprehensive review of a process to ensure accuracy and effectiveness.
Step-by-step explanation:
Among the given options, the one that best represents a walkthrough is d. The auditor traces three purchasing transactions from the purchase order to the financial statement for observation and understanding. A walkthrough is a step-by-step review of a process within an organization to assess the effectiveness of internal controls, ensure compliance with policies, and identify any areas of improvement. In this context, the auditor is performing the walkthrough by tracing transactions to understand the purchasing process and verify that it reflects correctly in the financial statements.