正解:A
Comprehensive and Detailed In-Depth Explanation:High employee turnover (A) poses the greatest risk because it leads to knowledge loss, operational disruptions, and potential security risks from departing employees. A constantly changing workforce can also impact compliance, training, and overall IT stability.
Other options:
* Lack of customer satisfaction surveys (B) is a business issue but not a critical IT risk.
* Aging staff (C) may be a long-term risk but does not have an immediate impact.
* Frequent software upgrades (D) can be beneficial if managed correctly.
Reference: ISACA CISA Review Manual, IT Governance and Management of IT