Get records based on multiple DropDownList from database in ASP.Net

Here i have three DropDownList but you can have more that that as per your requirement. But i am having only single OnSelectedIndexChanged event for them.

HTML:

<form id="form1" runat="server">
    <div>
        <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true" DataSourceID="SqlDataSource1"
            OnSelectedIndexChanged="DropDownList1_OnSelectedIndexChanged" DataTextField="LastName"
            DataValueField="EmployeeID">
        </asp:DropDownList>
        <asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="true" DataSourceID="SqlDataSource1"
            OnSelectedIndexChanged="DropDownList1_OnSelectedIndexChanged" DataTextField="LastName"
            DataValueField="EmployeeID">
        </asp:DropDownList>
        <asp:DropDownList ID="DropDownList3" runat="server" AutoPostBack="true" DataSourceID="SqlDataSource1"
            OnSelectedIndexChanged="DropDownList1_OnSelectedIndexChanged" DataTextField="LastName"
            DataValueField="EmployeeID">
        </asp:DropDownList>
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConString %>"
            SelectCommand="SELECT [EmployeeID], [LastName] FROM [Employees]"></asp:SqlDataSource>
        <br />
        <asp:TextBox ID="txtAddress" runat="server" TextMode="MultiLine" />
    </div>
    </form>

VB.NET:

Protected Sub DropDownList1_OnSelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
        Dim ddl As DropDownList = TryCast(sender, DropDownList)

        Dim constr As String = ConfigurationManager.ConnectionStrings("ConString").ConnectionString
        Using con As New SqlConnection(constr)
            Using cmd As New SqlCommand("SELECT Address FROM Employees WHERE EmployeeID = @EmployeeID", con)
                Using da As New SqlDataAdapter(cmd)
                    cmd.Parameters.AddWithValue("@EmployeeID", ddl.SelectedItem.Value)
                    con.Open()
                    Dim address As Object = cmd.ExecuteScalar()
                    con.Close()
                    Me.txtAddress.Text = address.ToString()
                End Using
            End Using
        End Using
    End Sub

Thank You.