(NP-PN-SBJ 
  (NR 巴拉克))
                    
(VP 
  (VV 可能)
                    
  (VP 
    (PP-TMP 
      (P 于)
                    
      (NP 
        (NT １２月)))
                    
    (VP 
      (VV 访美)))))
arg0: 
                    巴拉克          
                
argm: 
                    于 １２月