A、People who exercise more than half an hour. B、Soldiers at quite high places. C、People who do not exercise and sweat. D、Patient

If you’re confused about how much water you really need, I’m not surprised. Conflicting advice in recent headlines appears against the old "eight-a-day" advice. Is it necessary to swallow down eight glasses of water daily, or is this recommendation out of date? We’ve heard for years that eight glasses of water daily is the least amount necessary to keep healthy. And we’re warned of the danger of water shortage in our body without at least eight glasses. But, should each of us drink the same amount of water every day?(20)The answer is—you need what you need! If it’s summer, you need more. If you’re exercising, you need more.(19)If you’re a "normal" person who sits a lot, who is not sweating, and not exercising more than 15 to 20 minutes daily, you need no more than four glasses of water daily. Although the World Health Organization(WHO)recommends that everyone should drink a minimum of two liters of water daily, or about eight cups, the old "eight-a-day" rule is based on studies performed on people under special situations, including soldiers at quite high places and hospitalized patients.(20)What you and I need is different.
18. Which field does this passage belong to?
19. Who need no more than four glasses of water daily?
20. What can we learn about the amount of water that we should drink?