What can the determination of risk for a threat/vulnerability pair functionally express?

The determination of risk for a threat/vulnerability pair functionally expresses several critical aspects of information security, which is why the choice encompassing all possibilities is the correct answer.

By evaluating risk, organizations can assess the adequacy of their security controls. This involves understanding whether the existing measures are sufficient to mitigate specific threats and vulnerabilities. It helps in identifying potential weaknesses in the security framework and whether additional controls are required to protect against potential attacks.

Additionally, risk assessment encapsulates the impact of a threat-source. This means understanding what would happen if a threat were successfully realized, which is crucial for prioritizing security efforts and resource allocation.

Lastly, risk analysis also assesses the likelihood of a vulnerability being exploited by a specific threat actor. By determining how probable it is for a threat to leverage a vulnerability, organizations can better prepare and respond to potential incidents.

Since all these elements are integral to establishing a comprehensive understanding of risk, the option that states all choices are correct aligns well with the holistic approach to risk management in information security.