  
                
                       
                                   
                                                                         1980 1990                         
                              150       75                 
                                                          
                                  37  45                                           
                                                                                    
                    
                                                                                                            1949       1958           1966      1976                                        
                                                                                                                                                                                             
                                                                     
                                                                                                                    
                                                   