The most operationally efficient solution to centrally manage the partner network IP address ranges across multiple AWS accounts is to use a prefix list shared across accounts via AWS Resource Access Manager (AWS RAM). This approach allows for centralized management of IP address ranges, reducing the need to manually update security groups in each account. When a new partner is added, updating the prefix list automatically propagates the changes to all associated security groups across accounts. This method is more efficient than using DynamoDB or S3 with Lambda functions for updates, as it leverages AWS's native capabilities for resource sharing and management, minimizing operational overhead and potential for errors. Option C correctly implements this solution by creating a prefix list, sharing it across accounts using AWS RAM, and updating security groups to reference the prefix list. This ensures that any updates to the prefix list are automatically reflected in the security groups of all accounts, making it the most operationally efficient solution.