Which of the following is an early symptom of dehydration?

A. As previously noted, the length of the thoracic cavity increases, not decreases, during the contraction of inspiratory muscles.

B. The diaphragm moves downward (not upward) when it contracts, allowing the lungs to expand.

C. The contraction of the diaphragm and external intercostals increases the diameter of the thoracic cavity, providing space for the lungs to expand and fill with air. This is the correct answer.

D. The chest cavity does not compress the lungs during inspiration; instead, it expands to accommodate the lungs as they fill with air.

A. An increased pulse is a later symptom of dehydration, as the body attempts to maintain blood pressure and circulation when fluid levels are low.

B. Poor skin turgor is a sign of more advanced dehydration and is usually detected when skin remains tented after being pinched.

C. Decreased urinary output typically occurs as dehydration progresses and the body conserves water, but it is not usually the first sign.

D. Thirst is one of the earliest and most common symptoms of dehydration, as the body signals the need for water intake to restore fluid balance. This is the correct answer.