       
                        
                                          
                                                             
                                                                                                             
         
                                                                             
                                                                                       
                                                    
                                                                20                                            21                                                                                                                                                                                                                                                                                                                               
  1.            
              
                                                                          
                                                                                                                                                                                                  
   2.                                                               
                                    →  →                               
  3.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
                                                                                                                    
                   
              
                                                                                                                                                                                                                                                                                          
                                                                        