51. (    )

41. According to the passage, some doctors believe it is true that (   ). 

• A、you are healthy if cold-water swimming turns your skin color blue
  
  

• B、cold-water swimming causes more heart attacks in summer than in winter
  
  

• C、cold-water swimming can make the body temperature dangerously high
  
  

• D、Polar Bears are bears swimming in freezing water
  
  

12. The school has (   ) history of two (   ).

• A、/ ; hundred
  
  

• B、a; hundreds
  
  

• C、a ; hundred
  
  

• D、/; hundreds