What are common signs of dehydration?

The correct choice identifies thirst, dry mouth, and fatigue as common signs of dehydration because these symptoms are physiological responses to insufficient fluid intake. When the body is dehydrated, it loses the necessary fluids for various bodily functions, leading to an increased sensation of thirst as a signal from the brain to encourage fluid intake. A dry mouth results from the salivary glands not receiving enough water to produce saliva, making it difficult to swallow or speak comfortably. Fatigue is another common symptom, as dehydration can lead to reduced blood volume, which affects the body's ability to deliver oxygen and nutrients effectively to tissues, resulting in decreased energy levels and an overall feeling of tiredness.

In contrast, symptoms such as increased energy and appetite, frequent urination coupled with high energy, and headaches with improved concentration do not align with the physiological effects of dehydration. When the body is lacking proper hydration, rather than increased energy, individuals typically feel tired and sluggish.