20. —I usually go to school on foot. 

—Why don't you (   ) by bus for a change?

• A、try to go
  
  

• B、trying to go
  
  

• C、to try to go
  
  

• D、try going
  
  

23. (      )

• A、learnt
  
  

• B、worked
  
  

• C、remained
  
  

• D、studied
  
  

52. (    )