The auditor's next course of action should be to review the contract and DR capability of the cloud service provider. This will help the auditor to verify if the provider has a DR plan that meets the organization's requirements and expectations, and if the provider has evidence of testing and validating the plan annually. The auditor should also check if the contract specifies the roles and responsibilities of both parties, the RTO and RPO values, the SLA terms, and the penalties for non-compliance.
Reviewing the security white paper of the provider (option A) might give some information about the provider's security practices and controls, but it might not be sufficient or relevant to assess the DR plan. Reviewing the provider's audit reports (option B) might also provide some assurance about the provider's compliance with standards and regulations, but it might not address the specific DR needs of the organization. Planning an audit of the provider (option D) might be a possible course of action, but it would require more time and resources, and it might not be feasible or necessary if the contract and DR capability are already satisfactory. Reference:
Disaster recovery planning guide
Audit a Disaster Recovery Plan
How to Maintain and Test a Business Continuity and Disaster Recovery Plan

In multi-cloud environments, organizations use cloud services from multiple providers. This can lead to challenges in maintaining visibility and control over the data and services due to the varying management tools, processes, and security controls across different providers. The complexity of managing multiple service models and the reliance on different cloud service providers can reduce an organization's ability to monitor and control its resources effectively, thus increasing the risk of reduced visibility and control.
References = The information aligns with the principles outlined in the CCAK materials, which emphasize the unique challenges of auditing the cloud, including ensuring the right controls for confidentiality, integrity, and accessibility, and mitigating risks such as those associated with multi-cloud environments12.

The most useful document for an auditor to review when seeking visibility into the cloud supply chain for a newly acquired Software as a Service (SaaS) solution is the SaaS provider contract. The contract is the legal agreement that defines the terms and conditions of the cloud service, including the roles, responsibilities, and obligations of the parties involved1. The contract should also specify the service level agreements (SLAs), security and privacy requirements, data ownership and governance, incident response and reporting, audit rights and access, and subcontracting or outsourcing arrangements of the SaaS provider2. By reviewing the contract, the auditor can gain insight into the cloud supply chain and assess the risks, controls, and compliance of the SaaS solution.
The other options are not as useful as the SaaS provider contract. Payments made by the service owner are the financial transactions that reflect the fees or charges incurred by using the SaaS solution. They may indicate the usage or consumption of the cloud service, but they do not provide much information about the cloud supply chain or its security and compliance aspects3. SaaS vendor white papers are the marketing or educational materials that describe the features, benefits, or best practices of the SaaS solution. They may provide some general or technical information about the cloud service, but they are not legally binding or verifiable4. Cloud compliance obligations register is a tool that helps customers identify and track their compliance requirements and obligations for using cloud services. It may help customers understand their own responsibilities and risks in relation to the cloud service, but it does not necessarily reflect the compliance status or performance of the SaaS provider5.
Reference:
Cloud Services Due Diligence Checklist | Trust Center1, section on How to use the checklist Cloud Computing Security Considerations | Cyber.gov.au2, section on Contractual arrangements Cloud Computing Pricing Models: A Comparison - DZone Cloud3, section on Pricing Models What is a White Paper? Definition from WhatIs.com4, section on White Paper Cloud Compliance Obligations Register | Cyber.gov.au5, section on Cloud Compliance Obligations Register

Explanation
The General Data Protection Regulation (GDPR) is the regulation that is suitable if health information needs to be protected in the European Union. The GDPR provides the legal framework for the protection of personal data, including health data, and sets out directly applicable rules for the processing of the personal data of individuals1. The GDPR defines health data as personal data related to the physical or mental health of a natural person, including the provision of health care services, which reveal information about his or her health status2. The GDPR applies to any organization that processes health data of individuals who are in the EU, regardless of where the organization is established3.
The other options are not correct. Option B, DPIA, is incorrect because DPIA stands for Data Protection Impact Assessment, which is a process that helps organizations to identify and minimize the data protection risks of a project or activity that involves processing personal data. A DPIA is not a regulation, but a tool or a requirement under the GDPR4. Option C, DPA, is incorrect because DPA stands for Data Protection Authority, which is an independent public authority that supervises, through investigative and corrective powers, the application of the data protection law. A DPA is not a regulation, but an institution or a body under the GDPR5. Option D, HIPAA, is incorrect because HIPAA stands for Health Insurance Portability and Accountability Act, which is a US federal law that provides data privacy and security provisions for safeguarding medical information. HIPAA does not apply to the EU, but to the US6. References := European Health Data Space1 Article 4 - Definitions | General Data Protection Regulation (GDPR)2 Article 3 - Territorial scope | General Data Protection Regulation (GDPR)3 Data protection impact assessment | European Commission4 Data protection authorities | European Commission5 What is HIPAA? - Definition from WhatIs.com6