带div的Ajax面板

I am using asp.net c# to make a project. I need to make a part where i have a dropdown list which contains car models,which I get from my database. Afterwards I need to change a panel's content each time a new value is selected in the dropdown list(without refreshing the whole page).

I tried using the following code:

 <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" DataTextField="MODEL" Height="39px" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged" Width="151px">
        </asp:DropDownList>
<asp:ScriptManager id="ScriptManager1" runat="server"></asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>           
        <br />            
        <div id="finalDisplay" runat="server"></div>            
    </ContentTemplate>
    <Triggers>
    <asp:AsyncPostBackTrigger controlid="DropDownList1" EventName="SelectedIndexChanged" />
    </Triggers>
</asp:UpdatePanel>

I belive the structure which should be used here is updatePanel. So I need my div with id finalDisplay to display all the comments which are also stored on a database. Here is my code for it:

    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {

        //get car id from database
        string model = DropDownList1.SelectedValue.ToString();
        string sql1 = "SELECT CAR_ID FROM CARS WHERE MODEL='" + model + "'";
        string[] attr1 = { "CAR_ID"};
        List<String> cid = getList(sql1, attr1);
        string car_id = cid[0].ToString().Trim();
        //get all comments stored in the database for that car
        string sql2 = "SELECT USER_ID,CONTENT FROM COMMENTS where car_id='" + car_id + "'";
        string[] attr2 = { "CONTENT" };
        List<String> contents = getList(sql2, attr2);
        string class_names= "usernames";
        string class_contents= "contents";
        for (int i = 0; i < contents.Count-1; i++) {
            string uid = contents[i];
            string tmp_sql = "Select user_name from users where user_id='" + uid + "'";
            string[] tmp_attr={"USER_NAME"};
            List<String> tmp_list=getList(tmp_sql,tmp_attr);
            finalDisplay.InnerHtml += "<p class="+class_names+">" + tmp_list[0] + ":</p>";
            finalDisplay.InnerHtml += "<p class="+class_contents+">" + contents[i + 1] + "</p>";
            i = i + 1;
        }
    }

In the div with id finalDisplay nothing happens,it's empty. What am I doing wrong? It's my first time using ajax(if this is even ajax).

Move the DropDownList inside of the UpdatePanel.