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Scientists are always trying to find new green energy.Now ,some scientists in Swedenhave found one :the heat from our own bodies.They are putting together the heat that our bodies give off naturally,and using it to heat buildings.
       In general ,the temperature of the human body is about 36.8℃ and we are always giving off some heat.Our bodies are usually much warmer than the environment around us .When many people are together ,a lot of heat can be produced.
      About 250,000 people pass through Stockholm Central Station each day .Their bodies produce a lot of warm air.Usually,ventilator fans(換氣扇) would guide this warm air to the outside of the station and it would get lost .But Swedish scientists are using a piece of equipment to catch the warm air and guide it to heat underground water tanks (箱) .The warmed water from these tanks lets the heat enter an office building about 60 meters away.As a result ,the building’s energy costs are down by 20%.
      There are problems ,of course.“It’s very hard to move low-temperature heat very far,” saidLester LanefromCarnegieMelonUniversity.He said ,“don’t use more energy than you save when passing the warmed water on to another place.”
      The Swedish scientists also said that ,however ,it is not a big problem and ,after all,they want to use body heat more to heat homes and other buildings .This would make energy cheaper and the environment better . 
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(    ) 46.Which of the following is NOT true according to the passage?
A.We can use body heat to heat buildings.
B.The body heat is a kind of green energy
C.Many places are using body heat at present.
D.The temperature around us is usually lower than that of our bodies.
(    ) 47.How does our body heat offer us the service
① The heat makes underground water tanks become warmer
② The heat is passed on to enter an office building .
③ Use a piece of equipment to collect our body heat.
④ The temperature of the building is higher.
A.①②③④     B.③④②①     C.④③①②    D.③①②④
(    ) 48.If we spend $20 every month ,how much will we save every month after using the body heat as energy
A.$4.         B.$16         C.$20.            D.$40
(    ) 49.What’s the problem we face when we use our body heat
A.We can’t use body heat more
B.It can’t be passed on to a very far place.
C.It’s difficult to put the body heat together.
D.It may make our environment become worse.
(    ) 50.The underlined word “that ” in the last paragraph refers to “______”
A.how to collect body heat in public
B.how to use body heat to heat buildings
C.energy is much more expensive than body heat
D.moving low-temperature heat very far is very difficult.