how can I convert dataset to string from webservice

[thuy_t_bird]

this is from my webservice
[WebMethod]
public DataSet show()
{
String con = WebConfigurationManager.ConnectionStrings["thuy"].ToString();
SqlConnection sqlcon = new SqlConnection(con);
SqlDataAdapter da = new SqlDataAdapter("Select BranchName from branch", sqlcon);
DataSet ds = new DataSet();
da.Fill(ds, "branch");
return ds;
}

protected void Page_Load(object sender, EventArgs e)
{
Service s = new Service();
DataSet ds = s.show();
DropDownList1.DataSource = ds.Tables[0];
DropDownList1.DataBind();
}

and my Dropdowlist show:System.Data.DataRowView
Can you hep me please

Thuy