Final answer:
Reperformance of the control by the auditor provides the most assurance about the effectiveness of an operation of a control because it allows auditors to directly test the controls themselves.
Step-by-step explanation:
The most assurance about the effectiveness of the operation of a control in an audit would likely be provided by b. Reperformance of the control by the auditor. This technique allows the auditor to personally verify the accuracy and effectiveness of a control by independently executing it without relying on the entity's personnel. It eliminates the risk of biases or misrepresentations that may come with inquiries and observations.
While inquiry of entity personnel can provide insights, it is considered less reliable due to its subjective nature. Observation of entity personnel offers real-time evidence of controls in action, but it may not capture all instances, especially if the control is not consistently applied. A walkthrough includes a combination of techniques like observation, inquiry, and examination of documents, which offers a thorough look at a control but may not be as conclusive as directly reperforming the control.