13. I (   ) have handed in the report, but I (   ) not find the materials. 

• A、should; would
  
  

• B、should; could
  
  

• C、might; would
  
  

• D、would; could
  
  

33. (      )

• A、writes
  
  

• B、was writing
  
  

• C、has written
  
  

• D、had written
  
  

51. (    )