(IP 
  (NP-SBJ 
    (-NONE- *pro*))
                    
  (VP 
    (ADVP 
      (AD 也))
                    
    (VP 
      (VV 唱唱)
                    
      (NP-OBJ 
        (NN 圣诞)
                    
        (NN 歌)))))
arg0: 
                    *pro* 
                
arg1: 
                    圣诞 歌 
                
argm: 
                    也