This question asks for themain idea, which is the central message of the passage. The passage discusses several roles of water in the body, including temperature regulation, nutrient transport, and waste removal. It also highlights the effects of dehydration and the importance of monitoring fluid intake, particularly in older adults. All these details support one central idea: hydration is vital for maintaining overall health and proper body function. Option C correctly summarizes this main point. Option A is incorrect because the passage actually suggests older adults are at increased risk of dehydration. Option B contradicts the passage, which emphasizes water's importance. Option D is incorrect because the passage notes that thirst may decrease with age and is not the only indicator. On the NEX exam, main-idea questions often require recognizing repeated themes across the passage rather than focusing on one detail.
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