Another DDL and Textbox cleared question

 Budugu helped me with this post:
http://forums.asp.net/t/1456477.aspx
I'm back again because I don't know how to add an if...else clause to this statement:
' clears district DropDownList4.Attributes.Add("onclick", "document.getElementById('" + TxtDist.ClientID + "').value = '';") TxtDist.Attributes.Add("onclick", "document.getElementById('" + RadioBtnDist.ClientID + "').checked = true;") DropDownList4.Attributes.Add("onclick", "document.getElementById('" + RadioBtnArea.ClientID + "').checked = true;document.getElementById('" + TxtDist.ClientID + "').value = '';") ' clear doc DropDownList4.Attributes.Add("onclick", "do ...