1. They have been talking for the whole three hours.  (一般疑问句)
    _______ they _______  _______ for the whole three hours?
2. We have been living here for 12 years.  (改为同义句)
    We have been living here               12 years             . 
3. To spit in public places is not polite.  ( 同义句) 
                  isn't polite                            in public places.
4. We have been playing football for two hours.  (对划线部分提问)
    _______  _______ have you been playing football?
5. "Don't stand in the way," the policeman said to the boy. (根据句意进行改写) 
    The police told the boy                                         in the way.
6. He started to practice the guitar three hours ago.  (改成含介词for的同义句)
    He                            practicing the guitar for three hours.