after every next click drop down list data is getting doubled itself

[pranav thakur]

I am writting a c# code in asp.net for dropdown lists.
as follows:

public void function1()
{

SqlCommand cmd;
DataSet ds = new DataSet();
SqlDataAdapter ad = new SqlDataAdapter( );

cmd = new SqlCommand("Sel ect distinct client_name from client_list", cn);

ad.SelectComman d = cmd;
ad.Fill(ds, "client_lis t");
DropDownList1.D ataSource = ds;
DropDownList1.D ataTextField = "client_nam e";
DropDownList1.D ataBind();
}
public void function2()
{
SqlCommand cmd;
DataSet ds = new DataSet();
SqlDataAdapter ad = new SqlDataAdapter( );

cmd = new SqlCommand("Sel ect distinct site_location from client_list where client_name ='" + DropDownList1.S electedItem.ToS tring() + "'", cn);

ad.SelectComman d = cmd;
ad.Fill(ds, "client_lis t");
DropDownList2.D ataSource = ds;
DropDownList2.D ataTextField = "site_location" ;
DropDownList2.D ataBind();
}


after every next click drop down list data is getting doubled itself.
So can you plz help me to avoid this?

Thanks.