The best recommendation to include in an organization's bring your own device (BYOD) policy to help prevent data leakage is to require multi-factor authentication on BYOD devices. BYOD is a practice that allows employees to use their own personal devices, such as smartphones, tablets, or laptops, to access the organization's network, data, and systems. Data leakage is a risk that involves the unauthorized or accidental disclosure or transfer of sensitive or confidential data from the organization to external parties or devices.
Multi-factor authentication is a security measure that requires users to provide two or more pieces of evidence to verify their identity and access rights, such as passwords, tokens, biometrics, or codes. Multi-factor authentication can help prevent data leakage by reducing the likelihood of unauthorized access to the organization's data and systems throughBYOD devices, especially if they are lost, stolen, or compromised. The other options are not as effective as requiring multi-factor authentication on BYOD devices, because they either do not prevent data leakage directly, or they are reactive rather than proactive measures. References: CISA Review Manual (Digital Version)1, Chapter 5, Section 5.2.3

The risk that is most affected by this oversight is audit risk. Audit risk is the risk that the auditor may express an inappropriate opinion or conclusion based on the audit evidence obtained. Audit risk consists of inherent risk, control risk, and detection risk. Inherent risk is the risk that material errors or frauds exist in the audited area before considering the effectiveness of internal controls. Control risk is the risk that the internal controls fail to prevent or detect material errors or frauds. Detection risk is the risk that the auditor fails to identify material errors or frauds using the audit procedures performed. In this case, the auditor has overlooked evidence that could contradict a conclusion of the audit, which increases the detection risk and consequently the audit risk. References:
* CISA Review Manual (DigitalVersion), Chapter 2, Section 2.31
* CISA Online Review Course, Domain 1, Module 1, Lesson 32

The organization is primarily responsible for the security configurations of the deployed application's operating system when migrating its HR application to an Infrastructure as a Service (IaaS) model in a private cloud. This is because in an IaaS model, the cloud provider is responsible for the security of the underlying infrastructure that they lease to their customers, such as servers, storage, and networks, while the customer is responsible for the security of the areas of the cloud infrastructure over which they have control, such as operating systems, middleware, and applications. Therefore, the organization needs to ensure that the operating system is properly configured, patched, hardened, and monitored to protect the HR application from unauthorized access or malicious attacks.
The other options are not primarily responsible for the security configurations of the deployed application's operating system. The cloud provider's external auditor is not responsible for any security configurations, but rather for verifying and reporting on the cloud provider's compliance with relevant standards and regulations.
The cloud provider is responsible for the security of the underlying infrastructure, but not for the operating system or any software installed on it by the customer. The operating system vendor is responsible for providing updates and patches for the operating system, but not for configuring or securing it according to the customer's needs.
References:
* 11: What Is IaaS (Infrastructure As A Service)? - Forbes
* 12: What is Shared Responsibility Model? - Check Point Software
* 13: Who Is Responsible for Cloud Security? - Security Intelligence