distractors: can could don't
sentence: Soon the robot bird became old.It no longer sang beautiful songs.Just at that time,the emperor was ill and he became very weak.One morning,while 1ying  in bed,the emperor wanted it to sing once again .But the robot bird [MASK] sing any more.Suddenly,the nightingale landed on the window.She began to sing her most beautiful song.The emperor was very happy!He became  better and better  each day.