Default values in dependent combo box

Hi gurus,

           
     I have 3 combo boxes - Region, Country and City.

Whenever I select the label 'ALL' in Region, I want the same label 'ALL' to appear in the combo boxes Region and City by default (ie) ALL should appear in all the 3 combo boxes whenever ALL is selected in the Region combo box.

A chart showing some data should be displayed whenever the above combination appears.

Can anyone please tell me how this can be achieved?

Thanks in advance,

Regards,

Aparajitha