How to set the selected value for a dropdown list in an edit template?

I have a gridview that is populated from a sql datasource.   One of the columns is supposed to be editable, so I added a drop down list of possible values in the edititemtemplate.  However, how do I get the value that is their original selection to be selected when they click the edit button?  It's a list of various explanations, and instead of having the first explanation highlighted when they click edit (In alphabetical order), I want their current selection. 
Here's my code so far.  Is it possible to "bind" their current explanation as the selected explanation in ddExplanationPendingHR which is the dropdown box?
<asp:TemplateField HeaderText="Type:" SortExpression="Explanation"> <EditItemTemplate> <asp:DropDownList ID="ddExplanationPendingHR" runat="server" DataSourceID="dsGetExplanationCodes" DataTextField="Explanation ...