Thank you for writing.
At design time you can use the PropertyBuilder to add different types of columns and manage their properties. Please take a look at the following article, which describes how to work with it: http://www.telerik.com/help/winforms/gridview-design-time-support-property-builder.html
The column that you are looking for is GridViewComboBoxColumn: http://www.telerik.com/help/winforms/gridview-columns-gridviewcomboboxcolumn.html
I hope you find this information useful. Should you have any additional questions, do not hesitate to contact us.
the Telerik team
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