Как мы можем очистить данные в combobx2 при выборе следующего элемента в combobox1 с помощью C#

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hi,

I used two combo boxes cmbhospitals and cmbusers in cmbusers when i click hospital A in 1st combbox it displays users of that hospital but again when i click on hospital B in cmbusers(Combobox2) it was displaying both users og hospital A and B I used if which clears the text but not the previous hosptal data please suggest

Что я уже пробовал:

//cmbhusers.SelectedItem=null;
                  	   cmbhusers.Items.Clear();
                  	   cmbhusers.ResetText();
cmbhusers.selectedIndex=-1;

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