Water is important for many reasons. Between 55 and 75 percent of the body is water. Water is needed for cooling the body on hot days, and when we are working or exercising. Water carries body heat to the surface of the skin. 

Doctors say adults should drink about two liters of water a day to replace（替换） all the water lost in liquid waste and perspiration（出汗）. They say people should drink more than that in hot weather. It is important to drink before, during and after exercise. They say we should drink water even before we start to feel like we need something to drink. During hot weather, cool liquids（液体） are best. But don’t drink sweet drinks and alcohol.

Doctors also say it is possible to drink too much water. Some people, for example, do this if they exercise hard during a heat wave. The result is that the amount of water in the body increases. This causes cells（细胞） to become larger and sodium（钠） in blood to become too low. So when runners exercise or others work hard in hot weather, they’d better drink a sports drink with sodium in it. 

Doctors say actions other than drinking water can protect against the health dangers of heat. Eat fewer hot and heavy foods. If possible, cook foods during cooler times of the day. Also, rest more often. Physical activity produces body heat. These simple steps can prevent the health problems because of heat. They will prevent sickness, help you feel better and may even save your life.

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1.What is the main sentence of the first passage?

A Water is needed for cooling the body on hot days.

B Water carries body heat to the surface of the skin.

C Water is needed when we are exercising.

D Water is important for many reasons.

解析：选D。D 主旨大意题。通读第一段，就会判断出本段的主旨句在本段的开头，故选D。

2.In the passage, adults had better drink ________ a day.

A two liters of water

B two liters of sweet drinks

C 75liters of water

D 55 liters of water

解析：选A。A。细节理解题。由第二段的“Doctors say adults should drink about two liters of water a day to replace all the water lost in liquid waste and perspiration.”可知成年人每天应喝两公升的水。

3.Drinking too much water may make a person’s ________.

A body very strong

B work very good

C sodium in blood too low

D body too large

解析：选C。C。细节理解题。由第三段的“This causes cells to become larger and sodium in blood to become too low.”可知喝太多的水能使血液中的钠变得太低。

4.Doctors suggest runners to drink a sports drink in hot weather because _________.

A it has a lot of cells

B it has sodium

C it has rich sugar

D it has less heat

解析：选B。B。 细节理解题。由第三段的“So when runners exercise or others work hard in hot weather, they’d better drink a sports drink with sodium in it.”可判断这种运动型饮料中含钠。

5.According to the passage, which of the following is NOT TRUE?

A Physical activity produces body heat.

B Our body needs water when we exercise.

C The best drink is cool liquids in hot weather.

D We should drink water only when we want something to drink.

解析：选D。D。 综合性判断题。由最后一段的“Physical activity produces body heat.”判断A 与原文相符；由第一段的“Water is needed for cooling the body on hot days, and when we are working or exercising.”可判断B与原文相符；由第二段的“During hot weather, cool liquids are best.”可判断C与原文相符；由第二段的“They say we should drink water even before we start to feel like we need something to drink.”可判断D与原文不符；故选D。