Straight to your question - let's assume that you have two related RadComboBox control on your page. First RadComboBox will list the continents and the second RadComboBox will list the countries for the selected continent based on the first RadComboBox selection. In this case the data source for the second data source will filtered - this data source will contain only countries for the selected continent.
Then we add another pair of two RadComboBox controls on the page and you bind these RadComboBox controls to the same data source controls used for the RadComboBox controls in the first pair. Then the second RadComboBox control will be populated with the same filtered countries since the data source is already filtered by selecting a continent from the first RadComboBox in the fist pair.
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