(NP-SBJ 
  (-NONE- *pro*))
                    
(VP 
  (VC 是)
                    
  (VP 
    (VV 兼于)
                    
    (NP-OBJ 
      (NN 参考)
                    
      (CC 还是)
                    
      (NN 长官)
                    
      (NN 压力)))))
arg0: 
                    *pro*          
                
arg1: 
                    参考 还是 长官 压力