Which of the following is a common sign of dehydration?

Thirst, dry mouth, and decreased urine output are all hallmark signs of dehydration. When the body is dehydrated, it recognizes that fluid levels are inadequate, leading to an increased sensation of thirst as a natural response to encourage fluid intake.

Dry mouth is another symptom because inadequate hydration can affect saliva production. Decreased urine output occurs as the kidneys conserve water to maintain hydration status; this reduction in urine output is also often associated with concentrated urine, which may appear darker in color. Hence, the combination of these signs clearly indicates that the body is in a state of dehydration, signaling the need for rehydration in order to restore proper fluid balance.

In contrast, the other options do not accurately reflect common signs of dehydration. Increased blood pressure is generally not associated with dehydration, as it tends to drop due to reduced blood volume. Brightly colored urine can occur due to dehydration but is not a primary sign, and increased appetite is typically not related to dehydration. Therefore, the combination of thirst, dry mouth, and decreased urine output serves as a more definitive indicator of dehydration.