help > string code button clear for visual basic

I have project web application there are several dropdownlist. I am using visual studio express ..

I confused about string to clear button .. because I choose clear button. just text box cleared but dropdown not action to clear .

please help. thanks
 
following existing string.

Protected Sub btnclear_click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnclear.Click
cleartextbox(Me)
 Label11.Text = ""