How to make the one DropDownList Visible based on Selected Value of other DropDownList using JavaScript

how to make the other dropdown lists visible based upon the values selected  on one drop down lists.i have gn my code hich i tried kindly guide me

<tr>
            <td class="style33" align="right">
                How much Work experience do you have?<span class="style21">*</span>:</td>
            <td class="style34">
            
            <asp:UpdatePanel ID="UpdatePanel2" runat="server"> 
            <ContentTemplate>
                <asp:DropDownList ID="exp_select" runat="server" AutoPostBack="True" 
                    DataSourceID="SqlDataSource6" DataTextField="work_exp_select" 
                    DataValueField="work_exp_select" 
                    onselectedindexchanged="exp_txt_SelectedIndexChanged">
                    <asp:ListItem></asp:ListItem>
                    <asp:ListItem>Fresher</asp:ListItem>
                    <asp:ListItem>0</asp:ListItem>
                    <asp:ListItem>1</asp:ListItem>
                    <asp:ListItem>2</asp:ListItem>
                    <asp:ListItem>3</asp:ListItem>
                    <asp:ListItem>4</asp:ListItem>
                    <asp:ListItem>5</asp:ListItem>
                    <asp:ListItem>6</asp:ListItem>
                    <asp:ListItem>7</asp:ListItem>
                    <asp:ListItem>8</asp:ListItem>
                    <asp:ListItem>9</asp:ListItem>
                    <asp:ListItem>10</asp:ListItem>
                    <asp:ListItem>10 Above</asp:ListItem>
                    <asp:ListItem></asp:ListItem>
                    <asp:ListItem></asp:ListItem>
                    <asp:ListItem></asp:ListItem>
                    <asp:ListItem></asp:ListItem>
                    <asp:ListItem></asp:ListItem>
                    <asp:ListItem></asp:ListItem>
                </asp:DropDownList>
                <asp:SqlDataSource ID="SqlDataSource6" runat="server" 
                    ConnectionString="<%$ ConnectionStrings:subordinateConnectionString %>" 
                    SelectCommand="SELECT [work_exp_select], [work_exp_month] FROM [candidate_master]">
                </asp:SqlDataSource>
                <asp:SqlDataSource ID="SqlDataSource7" runat="server" 
                    ConnectionString="<%$ ConnectionStrings:subordinateConnectionString %>" 
                    SelectCommand="SELECT [work_exp_month] FROM [candidate_master]">
                </asp:SqlDataSource>
                <asp:DropDownList ID="Exp_months" runat="server" AutoPostBack="True" 
                    DataSourceID="SqlDataSource7" DataTextField="work_exp_month" 
                    DataValueField="work_exp_month">
                    <asp:ListItem></asp:ListItem>
                    <asp:ListItem>1</asp:ListItem>
                    <asp:ListItem>2</asp:ListItem>
                    <asp:ListItem>3</asp:ListItem>
                    <asp:ListItem>4</asp:ListItem>
                    <asp:ListItem>5</asp:ListItem>
                    <asp:ListItem>6</asp:ListItem>
                    <asp:ListItem>7</asp:ListItem>
                    <asp:ListItem>8</asp:ListItem>
                    <asp:ListItem>9</asp:ListItem>
                    <asp:ListItem>10</asp:ListItem>
                    <asp:ListItem>11</asp:ListItem>
                </asp:DropDownList>
                <asp:Label ID="monthlbl" runat="server" Text="month"></asp:Label>
                <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" 
                    ControlToValidate="exp_select" ErrorMessage="Enter Total Experience" 
                    ForeColor="Red"></asp:RequiredFieldValidator>
                </ContentTemplate>
                <Triggers>
<asp:AsyncPostBackTrigger ControlID="exp_select" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel><tr>
            <td class="style35" align="right">
                Which Industry you desire to work ?</td>
            <td class="style36">
                <asp:DropDownList runat="server" Height="33px" Width="486px" ID="industry_work" 
                    AutoPostBack="True" CausesValidation="True" DataSourceID="SqlDataSource3" 
                    DataTextField="industry_type" DataValueField="industry_type" 
                   >
                </asp:DropDownList>
                <asp:SqlDataSource ID="SqlDataSource3" runat="server" 
                    ConnectionString="<%$ ConnectionStrings:subordinateConnectionString %>" 
                    SelectCommand="SELECT [industry_type] FROM [industry_master]">
                </asp:SqlDataSource>
                &nbsp;&nbsp;<br />
                <asp:RequiredFieldValidator ID="RequiredFieldValidator15" runat="server" 
                    ErrorMessage="Enter Industry " ControlToValidate="industry_work" 
                    ForeColor="Red"></asp:RequiredFieldValidator>
                <br />
            </td>
            <td class="style36">
                </td>
        </tr>
        <tr>
            <td class="style7" align="right">
                Which Industry does your company belongs to?<span class="style21">*</span>:</td>
            <td>
                <asp:DropDownList ID="industry_txt" runat="server" Height="30px" 
                    Width="483px" CausesValidation="True" AutoPostBack="True" 
                    DataSourceID="SqlDataSource4" DataTextField="industry_type" 
                    DataValueField="industry_type">
                    <asp:ListItem>Select</asp:ListItem>
                    <asp:ListItem>IT</asp:ListItem>
                </asp:DropDownList>
                <asp:SqlDataSource ID="SqlDataSource4" runat="server" 
                    ConnectionString="<%$ ConnectionStrings:subordinateConnectionString %>" 
                    SelectCommand="SELECT [industry_type] FROM [industry_master]">
                </asp:SqlDataSource>
                <asp:RequiredFieldValidator ID="RequiredFieldValidator9" runat="server" 
                    ControlToValidate="industry_txt" ErrorMessage="please Enter Industry" 
                    ForeColor="Red"></asp:RequiredFieldValidator>
            </td>
            <td>
                &nbsp;</td>
        </tr>
        <tr>
            <td class="style11" align="right">
                Preferred Location to work ?<span class="style21">*</span>:</td>
            <td class="style12">
                <asp:DropDownList ID="prefered_location_txt" runat="server" Height="29px" 
                    Width="484px" DataSourceID="SqlDataSource1" DataTextField="city" 
                    DataValueField="city" AutoPostBack="True">
                    <asp:ListItem>Select</asp:ListItem>
                    <asp:ListItem>Chennai</asp:ListItem>
                </asp:DropDownList>
                 <asp:RequiredFieldValidator ID="RequiredFieldValidator10" runat="server" 
                    ControlToValidate="prefered_location_txt" 
                    ErrorMessage="please Enter Functional area" ForeColor="Red"></asp:RequiredFieldValidator>
            </td>
and the code for .cs

   protected void exp_txt_SelectedIndexChanged(object sender, EventArgs e)
    {
       // Label3.Text = exp_select.Text;

        if (exp_select.Text == "fresher")
        {
            Exp_months.Visible = false;
            monthlbl.Visible = false;
            industry_work.Visible = true;
            industry_txt.Visible = false;
            prefered_location_txt.Visible = false;
         
        }
        else
        {
            Exp_months.Visible = true;
            monthlbl.Visible = true;
            industry_txt.Visible=    true;
            prefered_location_txt.Visible = true;
            industry_work.Visible = false;
        }