Heaters should be kept going in the night for men to survive in polar areas.

• A、True
  
  

• B、False
  
  

• C、Not Given
  
  

As discovered by expedition scientists, Antarctica has not always been so cold as it is today, so has the Arctic.

• A、True
  
  

• B、False 
  
  

• C、Not Given
  
  

Task 2

21. In the twentieth century, soot          

22. If snow and ice covered areas begin melting,           

23. A soot forcing is unusually effective, which          

24. Hansen cautioned that greenhouse gases          

25. Warming in the Northern Hemisphere was large in at middle and high latitudes.           

A. produces much more global warming than a carbon-dioxide forcing of the same magnitude

B. contributed to 25 percent of observed global warming

C. winter and spring

D. the warming effects increase

E. still surpass soot in warming the world's climate during the last century

F. can be seen mostly in the Northern Hemisphere