问道英语题，稍微有点麻烦。英语高手帮帮忙，顺便告诉我点技巧~如果回答得好，我会追加的，谢谢！

问道英语题，稍微有点麻烦。英语高手帮帮忙，顺便告诉我点技巧~如果回答得好，我会追加的，谢谢！
If you don’t know how much water you need, I’m not surprised. Different advice in recent newspapers ，appears to be against the old“8-a-day”advice we all grew up with. Is it necessary to drink down eight glasses of water daily, or is this already out of date.?
We’ve heard for years that eight glasses of water daily is necessary for a person to keep healthy. Your weight loss and health depend on it. Drink eight glasses of water daily and see clearer skin, better sleep, and improve eyesight. We’re warned of losing water without at least eight glasses. But, there are some new ideas of examining your daily diet, including what you eat, as well as what you drink.
The answer is... you need what you need ! If it’ s summer, you need more. If you’ re exercising, you need more. If you’re a “normal”inactive person, and not exercising more than 15—20 minutes daily, you need no more than four glasses of water daily. Most drinks can be counted as part of your daily water intake. Although the World Health Organization suggests that eight cups, the old “8-a-day”rule is based on studies on people under difficult situations, including soldiers at high altitude and hospitalized patients, what you and I need is different.
17. Is the writer surprised if you don’t know how much water you need?
18. What does the old“8-a-day”advice mean?
19. Whom is the old“8-a-day”rule for? Give an example.
20. How much water do you really need according to the writer?
21. What is the article mainly about?
在线等，很急很急的问题~