47. What is the main subject of the passage?

• A、How to beat a bad mood. 
  
  

• B、How to talk bad moods out. 
  
  

• C、How to do physical exercises. 
  
  

• D、How to do aerobic exercise. 
  
  

55. (   )

39. If the information given in this passage is correct, when we look at a star at night (   ). 

• A、we will notice that it is not moving
  
  

• B、we cannot tell whether or not it still exists
  
  

• C、it is four years that the light we can see will reach us
  
  

• D、it will be brighter than the moon