Key performance indicators (KPIs) are measurable values that demonstrate how effectively an organization is achieving its key objectives. KPIs can be used to evaluate the progress and performance of a risk management program, as well as to identify the areas for improvement and alignment with the organization's strategy.
KPIs can provide the most useful information when determining a risk management program's maturity level, because they can reflect the extent to which the program is integrated, consistent, proactive, and value-adding.
KPIs can also be compared with industry benchmarks or best practices to assess the program's maturity level relative to other organizations. The other options are not as useful as KPIs, because they do not provide a clear and comprehensive picture of the risk management program's maturity level, but rather focus on specific aspects or outputs of the program. References = Risk and Information Systems Control Study Manual, Chapter 1, Section 1.3.2, page 18.

According to the CRISC Review Manual (Digital Version), the main reason to continuously monitor IT- related risk is to ensure risk levels are within acceptable limits of the organization's risk appetite and risk tolerance. The risk appetite is the amount and type of risk that an organization is willing to accept in pursuit of its objectives, while the risk tolerance is the acceptable variation in outcomes related to specific performance measures linked to objectives. Continuous monitoring is a process that tracks the security state of an information system on an ongoing basis and maintains the security authorization for the system over time.
Continuous monitoring helps to:
Provide ongoing assurance that the implemented security controls are operating effectively and efficiently Detect changes in the risk profile of the information system and the environment of operation Identify new or emerging threats and vulnerabilities that may affect the information system Support risk-based decisions by providing timely and relevant risk information to stakeholders Facilitate the implementation of corrective actions and risk mitigation strategies Promote accountability and transparency in the risk management process Enhance the security awareness and culture within the organization References = CRISC Review Manual (Digital Version), Chapter 4: IT Risk Monitoring and Reporting, Section 4.1: IT Risk Monitoring, pp. 213-2141

A KRI is a measure used by an organization to measure the health of a particular risk. In this case, the risk practitioner is developing a metric to measure the risk associated with security threats that were not identified by antivirus software12.
References
1Standardized Scoring for Security and Risk Metrics - ISACA
2Key Performance Indicators for Security Governance, Part 1 - ISACA

The most important factor when assessing the risk of allowing users to access company data from their personal devices is the classification of the data, as it indicates the level of sensitivity, confidentiality, and criticality of the data. Data classification helps to determine the appropriate level of protection and controls that are needed to prevent unauthorized access, disclosure, modification, or loss of the data. Data classification also helps to define the roles and responsibilities of the data owners, custodians, and users, and the acceptable use of the data. The other options are not the most important factors, although they may be relevant or influential in the risk assessment. The type of device may affect the security features and vulnerabilities of the device, but it does not determine the value or impact of the data. The remote management capabilities may affect the ability to monitor, control, or wipe the device in case of theft or loss, but they do not reflect the nature or purpose of the data. The volume of data may affect the storage capacity or performance of the device, but it does not indicate the importance or significance of the data. References = What is BYOD (Bring-Your-Own-Device) - CrowdStrike; Understanding BYOD Policy - Get Certified Get Ahead; Addressing cyber security concerns on employees' personal devices; Personal Devices at Work - Nonprofit Risk Management Center; 10 Keys to an Effective BYOD and Remote Access Policy