How to Select Multiple Items in the Dropdown in Windows Forms ComboBoxAdv(Classic)

In order to perform multiple selection, you can use the ComboboxAdv or MultiColumnComboBox controls, that contains a normal ListBox that allows you to select multiple items, internally.

//To select multiple items in ComboBoxAdv
this.comboBoxAdv1.ListBox.SelectionMode = SelectionMode.MultiExtended;
this.multiColumnComboBox1.ListBox.SelectionMode = SelectionMode.MultiExtended;
'To select multiple items in ComboBoxAdv
Me.comboBoxAdv1.ListBox.SelectionMode = SelectionMode.MultiExtended
Me.multiColumnComboBox1.ListBox.SelectionMode = SelectionMode.MultiExtended