Dropdown List Box Validations

<table>
<tr>
    <td>
    Select Country
    </td>
    <td>
    <asp:DropDownList ID="ddlCountry" runat="server" AutoPostBack="True" Height="16px" 
            onselectedindexchanged="ddlCountry_SelectedIndexChanged" Width="123px"></asp:DropDownList>
    </td>
    </tr>
     <tr>
    <td>
    Select State
    </td>
    <td>
    <asp:DropDownList ID="ddlState" runat="server" AutoPostBack="True" Height="16px" 
            onselectedindexchanged="ddlState_SelectedIndexChanged" Width="124px"></asp:DropDownList>
    </td>
    </tr>
     <tr>
    <td>
    Select City
    </td>
    <td>
    <asp:DropDownList ID="ddlCity" runat="server" Height="16px" Width="124px"></asp:DropDownList>
    </td>
    </tr>
    <tr>
    <td></td>
    <td>
    <asp:Button ID="btnSubmit" OnClientClick="return Validate()"  Text="Submit" runat="server" onclick="btnSubmit_Click" />
    </td>
    </tr>
    </table>

<script type="text/javascript" language="javascript">
        function Validate() {           
            var country = document.getElementById("ddlCountry").selectedIndex;
            var state = document.getElementById("ddlState").selectedIndex;
            var city = document.getElementById("ddlCity").selectedIndex;
           
            if (country <= 0) {
                alert("Please choose country");
                return false;
            }
            if (state <= 0) {
                alert("Please choose state");
                return false;
            }
            if (city <= 0) {
                alert("Please choose city");
                return false;
            }
        }
 </script>