Explanation
The auditor's next course of action should be to review the contract and DR capability of the cloud service provider. The contract should specify the roles and responsibilities of both parties regarding disaster recovery, as well as the service level agreements (SLAs) and recovery time objectives (RTOs) for the critical application. The DR capability should demonstrate that the cloud service provider has a plan that is aligned with the organization's requirements and expectations, and that it is tested annually and validated by independent auditors. The auditor should also verify that the organization has a process to monitor and review the cloud service provider's performance and compliance with the contract and SLAs.
Planning an audit of the provider (B) may not be feasible or necessary, as the auditor may not have access to the provider's environment or data, and may not have the authority or expertise to conduct such an audit. The auditor should rely on the provider's audit reports and certifications to assess their compliance with relevant standards and regulations.
Reviewing the security white paper of the provider may not be sufficient or relevant, as the security white paper may not cover the specific aspects of disaster recovery for the critical application, or may not reflect the current state of the provider's security controls and practices. The security white paper may also be biased or outdated, as it is produced by the provider themselves.
Reviewing the provider's audit reports (D) may be helpful, but not enough, as the audit reports may not address the specific requirements and expectations of the organization for disaster recovery, or may not cover the latest changes or incidents that may affect the provider's DR capability. The audit reports may also have limitations or qualifications that may affect their reliability or validity. References := Audit a Disaster Recovery Plan | AlertFind ISACA Introduces New Audit Programs for Business Continuity/Disaster ...
How to Maintain and Test a Business Continuity and Disaster Recovery Plan