The suggested answer is B.
The most important use of Key Risk Indicators (KRIs) is to provide an early warning signal. KRIs are designed to give advance notice of potential risk issues before they escalate into significant problems. By doing so, they enable management to take proactive measures to mitigate risks and prevent potential losses. While other uses, such as providing a backward-looking view on risk events, indicating risk appetite and tolerance, and enabling trend analysis, are valuable, the primary function of KRIs is to serve as an early warning mechanism.