Heading out for some exercise? You’ll take your shoes, socks, and a towel．You might take a music headset．But you’ll also need a bottle of water．Here is why．When you exercise, you sweat. Sweating is your body’s way of cooling down．The more you sweat, the more water your body loses．However, exercise also reduces thirst If you’re not thirsty, you may not drink enough water．You could lose too much water and become dehydrated(脱水)．A water loss of 10 percent can make you sick．A loss of 20 percent can kill you. So you need to be careful．
Here’s how to keep your body hydrated．About two hours before you exercise, drink one 500millilitre(1/2litre)bottle of water．Then drink another half bottle right before you begin．Drink water every 20 minutes as you exercise．You’ll need water long before you’re thirsty．
You need water even when you’re not exercising．You should drink about five bottles of water each day．Why so much? Your body cells are mostly water．So is your blood. Water helps your body to digest(消化)food and remove wastes．But your body loses water as you breathe, sweat, and urinate(排尿)．It loses about 2.5 liters (2,500 milliliters)of water each day．
You must replace the water your body loses．You can get water from many sources．Drinking water is the best source．Food and other fluids are good too, All food has some water in it．Fruit and vegetables are high in water Milk, juices, and other drinks also contain water．So take your pick．And remember to drink more water when you exercise．A happy body is a hydrated body．
(   )53．The passage suggests that each day you should drink           .
A．about 2,500 milliliters of water          B．about 500 milliliters of water
C．as much water as you can                D．only when you get thirsty
(   )54．What are some ways to replace water your body has lost?
A．Taking baths and eating eggs．      
B．Drinking juice and eating vegetables
C．Digesting food and removing wastes．
D．Eating many kinds of food and exercising．
(   )55．After reading the whole passage, we learn it is mainly about           ．
A．the results of research on dehydration 
B．water being important when we exercise
C．the importance of having enough water  
D．how much water our bodies lose ever day
(   )56．The author explains how to keep your body hydrated during exercise by presenting      .
A．some related numbers               B．the reasons why we need water
C．a series of steps you can follow        D．the results of experiments