              
                                                                                                                            
(  )                                      
                                                                                                                                
                                                                                                                                                                                                                                                                                                                                                                                                                                                         
(  )             
                                                                                                                                                                                                                                                                                 
( )                                                                                                                                                                                                                           ~xg                                                                                          —                                                                                                                                                                                                                                                                                                     
                                                                                                                                                                                                                                                                                                            
(  )           
                                                                                                                                                                                                                                                                                                                                                                                                                                            
                                                                                                                                                                                                            1998   10                                                            15                                                                                                                                                                                                                                                                                                    
                                                                            
2006   4                                                       171   17.5             2007   5                                                                      2008   3                                           17.3826                                                                                  —                    2001                                                                                                                                        