Ali,

>If I were need one more Combobox, I think I should use mmDataSet and add one DataView in my Cities business object, and I will use that DataView as BindingSourceDisplayMember. Is it true?

That's right...I'd forgotten that little tidbit I added to the Dev Guide that fixes the synchronization issue, but fortunately Jason remembered (now you know why he's an MM .NET MVP <s>).

Regards,