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__________ all the things we eat and drink, water is the most important. Not many people realize this, but it is quite true. The human body can live ___________ food for a long time, but two or three days without water usually leads to（导致）death. Many people do not understand how __________ water the human body needs at work and many people do not drink _________ especially in cold weather. Most people drink enough only in ___________ weather. Most people drink when they are ___________, but we often need more water, especially __________ doing exercise.
A man’s body contains 65%-75% water. Water is very important in several different __________. Most people need about five to seven liters（升）of water every day, but we do not need to drink that amount（量）, ____________ a lot of water comes from the food we eat. If we do not have enough water, however, we ____________ tired and may become ill.