A                                                                 
                                                                                                                                                                 
                                                                                                                                                                 
                                                                                                                                                                 
         yes                                                                                                                                                   no
                                                      decision                                                                                                   
                                                                                                                                                                 
                                                                                                                                                                 
                     B1                                                                                                                                       B2 
                                                                                                                                                                 
                                                                                                                                                                 
                                                                                                                                                                 
                                                                                                                                                                 
                                                                                                                                                                 
                                                                                                                                                                 
                                                                                               C