It should be D. If it has compatibility issue, then that can cause issue to DR plans

Inability to utilize the site when required

According to CRM 27th: Reciprocal agreements are agreements between separate, but similar, companies to temporarily share their IT facilities in the event that one company loses processing capability. Reciprocal agreements are not considered a viable option due to the constraining burden of maintaining hardware and software compatibility between the companies, the complications of maintaining security and privacy compliance during shared operations, and the difficulty of enforcing the agreements should a disagreement arise at the time the plan is activated." -> Key word is "compatibility" -> Answer D

The primary purpose of a reciprocal site for disaster recovery is to serve as a backup location to resume critical business operations in the event of a disaster. If the site cannot be accessed or utilized when needed due to various factors such as technical issues, contractual disputes, or resource constraints, the organization may face significant challenges in recovering from the disaster. This can lead to prolonged downtime, loss of revenue, damage to reputation, and potentially even business failure. Therefore, the inability to utilize the site when required represents the greatest risk to the effectiveness of the organization's disaster recovery strategy.