1.They spent 3 hours planting the trees.（改为同义句）    
It         them 3 hours                  the trees.
2.I'm allowed to buy books once a week. ( 对画线部分提问)    
                 are you allowed to buy books?
3.He can finish the work in two days.  (改为被动语态)    
The work                            in two days.
4.I think you should choose your own clothes.    
I                   you should choose your own clothes.
5.My parents allow me to go to the movies on weekends.  (对画线部分提问)
                 your parents allow you to           on weekends?