(IP 
  (NP-SBJ 
    (-NONE- *pro*))
                    
  (VP 
    (ADVP 
      (AD 都))
                    
    (VP 
      (VC 是)
                    
      (PP-PRD 
        (P 因为)
                    
        (IP 
          (IP 
            (NP-SBJ 
              (NN 农村))
                    
            (VP 
              (VV 贫无立锥)))
                    
          (PU ，)
                    
          (IP 
            (NP-SBJ 
              (NN 农民))
                    
            (VP 
              (ADVP 
                (AD 不得不))
                    
              (VP 
                (VP 
                  (VV 寄居)
                    
                  (PP 
                    (P 在)
                    
                    (NP 
                      (NP 
                        (CP 
                          (WHNP-1 
                            (-NONE- *OP*))
                    
                          (CP 
                            (IP 
                              (NP-SBJ 
                                (-NONE- *T*-1))
                    
                              (VP 
                                (VA 富裕)))
                    
                            (DEC 的)))
                    
                        (NP 
                          (NN 都市)))
                    
                      (NP 
                        (NN 底层)))))
                    
                (VP 
                  (VV 讨生活))))))))))
arg0: 
                    农民 
                
arg1: 
                    在 *OP* *T*-1 富裕 的 都市 底层 
                
argm: 
                    不得不