Final answer:
Thirst is an early sign of mild dehydration. It is important to hydrate at the first sensation of thirst to prevent the condition from worsening to moderate or severe dehydration, which can be dangerous and requires immediate medical intervention.
Step-by-step explanation:
If a person feels thirsty, dehydration has already started. The correct answer is a) Mild. When dehydration begins, the body starts to signal the need for fluids, typically through the sensation of thirst. It's important to start hydrating as soon as you feel thirsty to prevent the dehydration from escalating. Mild dehydration can develop into moderate or severe dehydration if not addressed. Symptoms of dehydration can include feeling thirsty, dry mouth, headaches, dark yellow urine, and dizziness. Severe dehydration is a medical emergency and requires immediate attention.