44. You shouldn't sit with your back towards the window because (   ). 

• A、the light is too bright
  
  

• B、the light is bad for your eyes
  
  

• C、you are in a dark room
  
  

• D、your book is in your shadow
  
  

15. Jack was happy that the train (   ) when he (   ) the station. 

• A、left; had arrived
  
  

• B、had not left; arrived
  
  

• C、had not left; had arrived
  
  

• D、left; arrived
  
  

51. (    )