_____ are the chief tools used to guide leaders in assessing an individual's fitness.

The correct answer highlights the importance of proper assessment tools in ensuring diver safety and fitness. NAUI's Risk Management Handbook and Medical History Form are vital resources used to evaluate a diver's physical and psychological wellness before undertaking diving activities. These documents help dive leaders identify any potential health issues that might affect a diver's ability to participate safely in diving.

NAUI’s Risk Management Handbook provides guidelines on how to manage and mitigate risks associated with diving, while the Medical History Form gathers essential information about a diver's past and current health conditions. This assessment is critical because even minor health issues can escalate underwater due to the nature of diving.

Diving logs and reports, while useful for tracking a diver's experience and time underwater, do not specifically assess fitness for diving. Diver training manuals provide educational materials but do not serve the function of assessing individual readiness. Emergency response plans are essential for preparedness in emergencies but do not contribute to the evaluation of a diver's fitness prior to diving activities. The focus on assessing fitness through appropriate tools ensures that diving remains a safe and enjoyable activity.