(NP-SBJ 
  (NN 调查)
                    
  (NN 单位))
                    
(VP 
  (ADVP 
    (AD 仍然))
                    
  (ADVP 
    (AD 无法))
                    
  (VP 
    (VV 断定)
                    
    (NP-OBJ 
      (CP 
        (WHPP-1 
          (-NONE- *OP*))
                    
        (CP 
          (IP 
            (NP-SBJ 
              (NN 事故))
                    
            (VP 
              (PP-PRP 
                (-NONE- *T*-1))
                    
              (VP 
                (VV 发生))))
                    
          (DEC 的)))
                    
      (NP 
        (NN 原因)))))
arg0: 
                    调查 单位          
                
argm: 
                    仍然          
                
argm: 
                    无法          
                
arg1: 
                    事故 发生 的 原因