Which of the following is a key sign of heat exhaustion?

Excessive sweating is indeed a key sign of heat exhaustion. This condition typically occurs when the body becomes overheated, often due to prolonged exposure to high temperatures or vigorous physical activity. The body's natural cooling mechanism involves sweating, which helps to regulate temperature by evaporating sweat from the skin. In cases of heat exhaustion, the individual often sweats profusely as their body attempts to cool itself down in response to the heat stress.

While other signs such as increased heart rate can be associated with heat exhaustion, excessive sweating is a more direct indicator that the body is struggling to maintain a safe temperature and can lead to dehydration if not addressed promptly.